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Fine structure of postgonopodial glands of a myriapod Glomeris marginata (Villers)
TISSUE Puhlirhctl
& CELL
1976 8 (2) 293-304
b,r Lon.gtncrn Group Ltd. Printed
in Greut Britain
LYSIANE
JUBERTHIE-JUPEAU
FINE STRUCTURE OF POSTGONOPODIAL GLANDS OF A MYRIAPOD GLOMERIS MARGINATA (VILLERS) ABSTRACT. The postgonopodial gland of the myriapod Glomvris murginatcr (Villers), which produces a pheromone, is an integumentary gland comprising numerous functional secretory units. Each secretory unit consists of two proximal secretory cells, an intermediary cell lacking secretory characteristics and a canal cell surrounding the canal, which is secretory in nature. Secretory proximal cells exhibit a zone of small channels originating from invaginations of the plasma membrane and through which secreted material is released. Apposing each invagination of these cells is a corresponding invagination of the intermediary cell: the two units in the centre of the intermediary cell join another which communicates with the canal. Secretion produced by the latter passes through the canal wall and blends with secretion of the two proximal cells. The most striking feature of all these cells is the abundance of tubules and fibrils in the small canal zone in the proximal cells, which also exhibits a centriole; in the intermediary cell around cytoplasmic membrane invaginations where a diplosome is present, and in almost the entire canal cell.
Introduction
Glomerid species Glomeris marginata and G. intermedia, in Trachysphaera orghidani and in Glomeridella kervillei. These glands originate from hypodermal cells without any differentiation of an integumentary invagination: this invagination appears behind the last pair of legs (the gonopods) at the ‘prematurus’ stage. These authors showed, furthermore, that in animals fixed in copula the fluid secreted by postgonopodial glands is greatly extravasated. According to Haacker (1969) the secretion produced beneath the female’s mouthparts at the beginning of mating is licked by the female while the final position of mating is established. The main function of this secretion seems to be that of an arrestant.
IT has been found that the mating behaviour
in many species of Diplopoda involves communicative patterns between the male and the female. These may involve mechanical signals, for example, the touching of the female (Kinkel, 1955; Demange, 1959; Mauries, 1969), drumming on the ground (Haacker, 1971) and stridulation performed by the male (Haacker, 1970). In particular, the mating position, which permits the introduction of gonopods by the male, is achieved due to a secretion of glands that are variously located in different genera: coxal glands in some Iulids, dorsal glands in Chordeuma and postgonopodial glands in some Glomeridae, Trachyspheridae and Glomeridellidae. A histological study of postgonopodial glands, discovered by Juberthie-Japeau and Tabacaru (1968) was carried out in the
Materials and Methods
Postgonopodial were fixed phosphate 0~04 in embedded
Laboratoire souterrain du Centre National de la Recherche Scientifique, 09410 Moulis, France. Received 28 October Revised 27 February
glands
of adult
marginata, collected in February
1975. 1976. 293
Glomeris
and May, in 2.9% glutaraldehyde in 0.1 M buffer, and postfixed in 29,, the same buffer. Glands were in Epon 812. Thin sections were
____________
cu.
------______
Ce.
.Z.G.
-2.M.
POSTGONOPODIAL
GLANDS
OF
A MYRIAPOD
cut with a diamond knife on a Reichert OM U2 Ultramicrotome, and contrast was enhanced with uranyl acetate and lead citrate. Staining of polysaccharides was performed with TC H proteinate silver after periodic oxidation (Thiery, 1967). Sections were examined in a Sopelem electron microscope operated at 50 kV. Results Getlerul structure
qf the gland
Each male possesses a postgonopodial gland which opens ventrally between the bases of the nineteenth pair of legs and the anal valves, in a very wide opening behind which is located a flat, forwardly directed efferent duct. The enlarged terminal part of this duct constitutes the reservoir. The gland, which is mammillated in appearance, is situated around the reservoir between the end of the nerve cord and the rectum. It is dorsoventrally flattened and is about 300 y in thickness, 700 IL in length and 600 p in width. In sagittal section, the gland is arranged as follows: the central part is occupied by the reservoir filled with secretory product and limited by a porous cuticle; beneath the cuticle lie numerous canals which are often piled up and interdigitating. The periphery of the gland is occupied by the voluminous secretory cells, resting on a basal lamina; some canals can be seen at this level. Ulrrcrstructurnlstudy The glandular region situated around the reservoir is composed of secretory units which are contiguous and identical. Each of these (Fig. I) consists of two proximal secretory cells lying side by side, each having an excretory channel formed by invagination of the plasma membrane. These two channels unite in the neighbouring
‘95
cell, the intermediary cell, which lies opposite the two proximal cells. As before, this channel is limited by a plasma membrane invagination; the channel lumen is extended by an epicuticular canal which enters the canal cell. The latter is elongated and exhibits secretory characteristics. It surrounds the canal as far as the middle of the cuticle after which point the canal is defined only as an epicuticular invagination into the cuticle. Interspersed with the canal cells are glycogenrich cells, the cytoplasm of which is extensive and ramifying. Study qf’reservoir cuticle The reservoir is limited by a cuticle 6--X p in thickness. The most external region (Fig. 12) is a multilayered epicuticle: the outermost layer is very electron dense and is followed in sequence by an electron-lucent layer, another layer of high electron density thicker than the first, and possibly a second lucent layer. A thin exocuticle appears to be present under the epicuticle and above a thick lamellate endocuticle showing the characteristic ‘parabolic’ appearance. The distal part of the canals is three-layered, the central layer being less dense than the other two (Figs. 13, 14). Study qf’cr secretory wit (a) The two proximal cells (Figs. I --7). These are unusually large (40-50 p in height and cu. 20 p in width) and are always filled with secretory granules. The nucleus (Fig. 4) is generally situated in the basal third of the cell; it is irregularly shaped and possesses finely granular chromatin distributed throughout the matrix and two large, generally peripheral and heterogeneous nucleoli. The cytoplasm is characterized by the grouping of some of its organelles. The proximal part of the cell includes a
Fig. I. Diagram of one glandular unit of the postgonopodial gland; C, centriole; CC, canal cell; Cc,, excretory cdnal of the glandular unit; CG, glycogen cell; CI, intermediarv _ cell: CS. .uroximal secretorv . cell: Cu. cuticle: D, desmosome: /Ii. diolosome; I, granule with rods of dense material; R, reservoir; RG, rough endoplaimic reticulum. ZC, small channel zone; ZG, Golgi zone; ZM, mitochondrial zone.
JUBERTHIE-JUPEAU
region containing little other than abundant cisternae of the endoplasmic reticulum (Fig. 3) which are in places very dilated. Rough ER cisternae are also seen between the secretory granules. In some cells, the contents of the ER cisternae are only slightly electron dense, and in this case the overall appearance of the cell is very clear. Other cells exhibit ER cisternae containing very opaque material, thereby appearing denser than the preceding cell types. The mitochondria (Fig. 3) are, for the most part, grouped in a single zone adjoining the nucleus. Here, they are closely packed in cytoplasm devoid of other components except for occasional vesicles of the rough ER. These mitochondria are small and more or less flexuous and possess sparse narrow cristae. The Gogli complexes (Fig. 4) are grouped into a spherical zone and the externallylocated forming face of each complex frequently shows dilated cisternae. Their activity gives rise to numerous electrondense vesicles that migrate towards the centre of the Golgi zone. Successive aggre-
gation of these vesicles produces subspherical masses, sometimes very heterogeneous, which are probably the origin of the secretory granules. Furthermore, in the centre of some Golgi zones occur secretion droplets resembling those present in other parts of the cytoplasm. The secretory granules (Figs. 2, 3) occupy most of the cytoplasm, and in particular, they are clustered in a fourth area-the small channel zone (Figs. 2, 5). This very specialized area is situated around the excretory channel of the cell. This channel is very short, and divides into small tortuous channels which in turn divide again in a region where the cytoplasm contains many microtubules and filaments and lacks other cell components (Fig. 2). The entire small channel system forms an extracellular cavity. Secretory granules reach the margin of this zone. A centriole is always present at the edge of this area: this presents the usual nine triplets (Fig. 7), however microtubule A in each triplet possesses an extra microtubule on its internal aspect. The two secretory cells of each unit are
Fig. 2. Section through the proximal secretory cells (CS) in the small channel zone (ZC) and through the intermediary cell (CI) of a glandular unit; C, centriole; D, desmosome; S, secretory granule; ZF, fibrillar zone around the central channel (Cp) of the intermediary cell. x 15,000. Fig. 3. Basal part of a proximal secretory cell. MB, basal lamina; S, secretory RG, rough endoplasmic reticulum; ZM, mitochondrial zone. x 18,000.
granule;
Fig. 4. A section of the nucleus (N) and the Golgi zone (ZG) of a proximal cell. S, secretory granule. x 6600.
secretory
Fig. 5. Proximal secretory cell (CS) and intermediary cell (CI). The excretory channel of the secretory cell which is formed by an invagination of the plasma membrane and the small channels are situated in a fibrillar zone called the small channel zone (ZC). A secretory granule (S) largely surrounded by filaments is about to pass into the channel. In the fibrillar zone (ZF) of an intermediary cell is a channel Ct adjoining that of the secretory cell Cx and the perpendicular channel Cp seen in transverse section; D, desmosome. x 32,000. Fig. 6. Secretory x 24,000.
granule(S)
of a proximal
secretory
cell approaching
Fig. 7. Centriole of a proximal secretory cell. Note nine triplets, which are associated with a surnumerary tubule. x 63,000.
a small channel. the A tubules
of
Fig. 8. Intermediary cell showing the two transverse channels (Ct) facing the excretory channel (Cx) of a proximal secretory cell. These two unite to form a perpendicular channel (Cp); D, desmosome; ZF, fibrillar zone. x 43,000.
POSTGONOPODIAL
GLANDS
OF A MYRIAPOD
contiguous except at their contact with the intermediary cell, and are symmetrically placed with respect to the latter. In particular, the small channel zone faces each side of the intermediary cell. (b) The intermediary cell. This small cell is located between the two previously described (Figs. 1, 2, 8). Its membrane is invaginated adjacent to the small channel zone of each secretory cell. Thus two channels are situated in front of the excretory channel of each secretory cell (Fig. 8). The two channels of the intermediary cell unite centrally to produce one perpendicular channel. The latter is cu. 3000 8, in diameter and scarcely 2 p in length and reaches the base of the adjoining canal cell (Fig. 9). lintil it reaches the level of the canal cell, the secretory product of proximal cells is contained only by the plasma membrane of the intermediary cell. The central part of these cells, in effect, is traversed by channels forming an inverted T: it is subspherical and contains only densely packed microtubules and filaments which are interspersed, and surround the channels (Fig. 8). This region of the intermediary cell is linked to the secretory cells by an extremely well-developed desmosome. This is dome-shaped, and in the centre the channels of secretory and intermediary cells anastomose. Adjacent to this desmosomal complex are present septate junctions, beyond which no special junctions are differentiated. Around the fibrillar central part of the cell a narrow zone of cytoplasm is present, except at the level of the nucleus. The latter is extensively lobed, and condensed chromatin is distributed in patches. A diplosome is always present at the margin of the fibrillar zone. (c) The curzal cefl. This cell (Figs. 1, 9-l 1, 14417), the proximal region of which adjoins the intermediary cell and the distal part of which penetrates the cuticular reservoir, exhibits along its entire length a cavity that ensheaths the canal. The wall of the canal can be seen just at the end of the channel of the intermediary cell: this is a tube of electron-lucent homogeneous material which maintains a similar structure up to the epicuticular invagination. Beyond the inter-
299
mediary cell the secretory product passes into the lumen of a true canal which is ca. 4500 A in diameter and is without a bulb. The canal cell shows deep invaginations of the plasma membrane adjoining the entire length of the canal (Figs. 10, 11). These invaginations are wide and more or less cylindrical along almost the entire length and are filled with homogeneous material of low electron density which contains small subparallel rods of much denser material. In the subdistal part of the cell, very deep and flat infoldings surround large mitochondria (Fig. 14). The nature of the canal changes between the regions withand without mitochondria. The homogeneous part of the canal forms a pad beyond which it displays the three-layered epicuticular pattern (Fig. 15): the cytoplasm at this level exhibits several bundles which are perhaps fibrillar and which are bent and arranged in a spoke-like fashion (Fig. 16). The canal cell is enlarged in the basal region where the nucleus is located. Within the cytoplasm, microtubules are oriented along the long axis of the cell and are most numerous in the apical region. In addition, the cytoplasm contains active Golgi complexes, small mitochondria, numerous free ribosomes and short cisternae of the rough ER. The last are sometimes arranged in rings and appear to be engaged in secretion, but the origin of secretory product in invaginated cavities has not been determined. (d) The glycogen cells. These ensheath the canal cells almost throughout their entire length, except at the level of the cuticle. They display a very extensive cytoplasm, dissected into thin flanges that penetrate between canal cells. The nucleus of these cells may be situated at various levels; it is always irregular in shape, and includes chromatin of low electron density in the peripheral nucleoplasm. The cytoplasm contains free ribosomes, some rough ER cisternae, small mitochondria, microtubules and, in particular, large amounts of glycogen dispersed throughout the ceil. Granules of glycogen are frequently clustered in clear areas of cytoplasm (Fig. IO). Release qf’secretory products qfproximul cells The whole area of the small channels proximal secretory cells corresponds
of the to an
JUBERTHIE-JUPEAU
extracellular cavity, as in most other integumentary glands previously described. The secretory granules are released into the small channels: prior to release the granules within the small channel zone are surrounded on all sides by microtubules and many filaments, and come into contact with the surface of a small channel. Fusion of the membrane limiting the secretory granule and that of the small channel takes place (Figs. 5, 6), and the content of the granule passes into the channel. The microtubules and filaments may play a mechanical role in this process. Discussion
In Myriapoda, the fine structure of a pheromone-producing gland, the secretion of which performs a communicative function in mating behaviour, is here studied for the first time. As in all integumentary glands of arthropods, postgonopodial glands of Glomeris
marginata are made up of a large number of
secretory units, joined together. The secretory product of each of these units is released into a common reservoir connected to the exterior via a wide duct. Each glandular unit is partially ensheathed by cells containing glycogen. Each unit consists of two proximal secretory cells, an intermediary cell without secretory characteristics and a canal cell which is secretory in nature. The proximal secretory cells are very uniform in structure and are closely associated; each possesses a small excretory channel formed by imagination of the plasma membrane which ramifies to form an extracellular cavity. Each glandular unit, displaying an exto ‘Class 3’ cretory canal, corresponds epidermal glands as defined by Noirot and Quennedey (1974). Each could originate, as in all dermal glands of insects (Delachambre, 1973) from a gland similar to the type B dermal glands of Rhodnius (LaiFook. 1970) and exhibits a secretory cell
Fig. 9. Section showing the positions of the two proximal secretory cells (CS), of the intermediary cell (Cl) and of the basal part of the canal (CC); Ce, canal filled up with a secretory product; D, desmosome; N, nucleus of intermediary cell; SC, secretory product of the canal cell; ZC. small channel zone. x 17,000. Fig. 10. Transverse section through the canal cell. Ce, canal; of the canal cell; CG, glycogen cell; m, microtubules. x 32,000.
SC, secretory
product
Fig. 11. Transverse x 32,000
SC, secretory
product.
section through
the canal cell. Ce, canal;
Fig. 12. Canal (Ce) opening into the reservoir Cu, cuticle; S, secretory product. x 32,000. Fig. 13. Transverse Fig. 14. Transverse cytoplasmic processes.
(R) of the postgonopodial
section of the canal beneath section through x 28,000.
apical
part
its aperture. of canal
Cu, culicle.
gland. x 32,000
cell. Cu, cuticle;
DC,
Fig. 15. Subapical part of the canal cell (CC) shown facing the invaginations without any mitochondria (Di), the epicuticular structure of the canal and, facing the invaginations with bulky mitochondria (Dm), the homogeneous structure of the canal. x 32,000. Fig. 16. Transverse section of the canal cell between the invaginations with large mitochondria and the invaginations Jacking mitochondria; E, fibrillar bundles around the canal; Cu, cuticle. x 43,000. Fig. 17. Transverse section M, mitochondria. x 43,000.
of the canal
cell at the level of large mitochondria.
PDSTGOhOPODlAL
GLANDS
OF
A MYRIAPOD
10I
0 15
POSTGONOPODlAL
GLANDS
OF A MYRIAPOD
with an extracellular cavity in connection with the lumen of a canal secreted by one or more cells. The extracellular cavity of G. murginatu resembles the branched extracellular chamber of the accessory salivary glands of the Tettigoniid Homovocovyphus uitiddus. The canal of G. marginatrr is secreted by one cell, secretory in nature. Two secretory cells are present, and between them and the canal cell is located an intermediary ceil. As far as cytoplasmic organelles are concerned, the most prominent feature of organization is the great development of microtubules and filaments especially in the small channel zone of the secretory cells, in the central region of the intermediary cell and in the canal cell. A centriole is always present in each secretory cell and a diplosome in the intermediary cell. These are located at
w
the margin of a zone of filaments. The centriole of the proximal secretory cells is unusual: it displays the classical nine triplets pattern but the A tubule is equipped with a supernumerary tubule on its inner face. No direct relationship can be seen between tubules of centrioles and cytoplasmic microtubules; it is only possible to note their proximity and constancy. The release of secretory granules into a small channel occurs when a granule is surrounded by microtubules and filaments and following membrane fusion. i.e. by exocytosis. The proximal secretory cells empty their product into the lumen of the small channels and thence the canal without any filtration, but the secretory product of the canal cell must pass through the canal wall. The two secretory products are blended before reaching the reservoir
JUBERTHIE-JUPEAU
304
References ANSTEE, J. H. 1975. The fine structure of the ‘accessory glands’ of the Tittigoniid, Homorocoryphus niridus. J. Insect Physiol., 21, 1211-1217. DELACHAMBRE,J. 1973. L’ultrastructure des glandes dermiques de Tenebrio molitor L. (Insecta, Coleoptera). Tissue & Cell, 5, 243-257. DEMANGE,J. M. 1959. L’accouplement chez Graphidostreptus tumuliporus (Karsch) avec quelques remarques sur la morphologie des gonopodes et leur fonctionnement. Bull. Sot. eat. Fr., 66, 198-207. HAACKER, U. 1969. Spermaiibertragung von Glomeris (Diplopoda). Naturwissenschaften, 56,467. HAACKER, U. 1970. Der Stridulationsapparat von Loboglomeris und seine Funktion im Sexualverhalten. Vie Milieu (C), 20, 57-64.
HAACKER, U. 1971. Trommelsignale bei Tausendftisslern. Naturwissenschaften, 58, 59-60. HAACKER, U. 1972. Communication in courtship and mating behaviour. Symp. Zool. Sot. London (1974), 32, 317-328. JUBERTHIE-JUPEAU,L. et TABACARLJ,1. 1968. Glandes postgonopodiales des Oniscomorphes (Diplopodes, Myriapodes). Revue Ecol. Biol. Sol, 5 (4), 605-618. KINKEL, H. 1955. Zur Biologie und Okologie des getiipfelten Tausendfusses Blaniulus guttulafus gerv. Z. angew. Eat., 37,401-436. LAI-FOOK, J. 1970. The fine structure of developing type ‘B’ dermal glands in Rhodnius prolixus. Tissue & Cell, 2, 119-138. MAURIES, I. P. 1969. Observation sur la biologie (sexualit&, p&riodomorphose) de Typhloblaniulus lorifer consoranensis BrGlemann. Diplopoda, Blaniulidae. Ann. SpPIPol., 24,495-504. NOIROT, Ch. and QUENNEDEY, A. 1974. Fine structure of Insect epidermal glands. Annu. Rev. Entomol., 19,6l-80. THIERY, J. P. 1967. Mise en evidence des polysaccharides sur coupes fines en microscopic blectronique. J. Microsc., 6, 987-1018.
& CELL
1976 8 (2) 293-304
b,r Lon.gtncrn Group Ltd. Printed
in Greut Britain
LYSIANE
JUBERTHIE-JUPEAU
FINE STRUCTURE OF POSTGONOPODIAL GLANDS OF A MYRIAPOD GLOMERIS MARGINATA (VILLERS) ABSTRACT. The postgonopodial gland of the myriapod Glomvris murginatcr (Villers), which produces a pheromone, is an integumentary gland comprising numerous functional secretory units. Each secretory unit consists of two proximal secretory cells, an intermediary cell lacking secretory characteristics and a canal cell surrounding the canal, which is secretory in nature. Secretory proximal cells exhibit a zone of small channels originating from invaginations of the plasma membrane and through which secreted material is released. Apposing each invagination of these cells is a corresponding invagination of the intermediary cell: the two units in the centre of the intermediary cell join another which communicates with the canal. Secretion produced by the latter passes through the canal wall and blends with secretion of the two proximal cells. The most striking feature of all these cells is the abundance of tubules and fibrils in the small canal zone in the proximal cells, which also exhibits a centriole; in the intermediary cell around cytoplasmic membrane invaginations where a diplosome is present, and in almost the entire canal cell.
Introduction
Glomerid species Glomeris marginata and G. intermedia, in Trachysphaera orghidani and in Glomeridella kervillei. These glands originate from hypodermal cells without any differentiation of an integumentary invagination: this invagination appears behind the last pair of legs (the gonopods) at the ‘prematurus’ stage. These authors showed, furthermore, that in animals fixed in copula the fluid secreted by postgonopodial glands is greatly extravasated. According to Haacker (1969) the secretion produced beneath the female’s mouthparts at the beginning of mating is licked by the female while the final position of mating is established. The main function of this secretion seems to be that of an arrestant.
IT has been found that the mating behaviour
in many species of Diplopoda involves communicative patterns between the male and the female. These may involve mechanical signals, for example, the touching of the female (Kinkel, 1955; Demange, 1959; Mauries, 1969), drumming on the ground (Haacker, 1971) and stridulation performed by the male (Haacker, 1970). In particular, the mating position, which permits the introduction of gonopods by the male, is achieved due to a secretion of glands that are variously located in different genera: coxal glands in some Iulids, dorsal glands in Chordeuma and postgonopodial glands in some Glomeridae, Trachyspheridae and Glomeridellidae. A histological study of postgonopodial glands, discovered by Juberthie-Japeau and Tabacaru (1968) was carried out in the
Materials and Methods
Postgonopodial were fixed phosphate 0~04 in embedded
Laboratoire souterrain du Centre National de la Recherche Scientifique, 09410 Moulis, France. Received 28 October Revised 27 February
glands
of adult
marginata, collected in February
1975. 1976. 293
Glomeris
and May, in 2.9% glutaraldehyde in 0.1 M buffer, and postfixed in 29,, the same buffer. Glands were in Epon 812. Thin sections were
____________
cu.
------______
Ce.
.Z.G.
-2.M.
POSTGONOPODIAL
GLANDS
OF
A MYRIAPOD
cut with a diamond knife on a Reichert OM U2 Ultramicrotome, and contrast was enhanced with uranyl acetate and lead citrate. Staining of polysaccharides was performed with TC H proteinate silver after periodic oxidation (Thiery, 1967). Sections were examined in a Sopelem electron microscope operated at 50 kV. Results Getlerul structure
qf the gland
Each male possesses a postgonopodial gland which opens ventrally between the bases of the nineteenth pair of legs and the anal valves, in a very wide opening behind which is located a flat, forwardly directed efferent duct. The enlarged terminal part of this duct constitutes the reservoir. The gland, which is mammillated in appearance, is situated around the reservoir between the end of the nerve cord and the rectum. It is dorsoventrally flattened and is about 300 y in thickness, 700 IL in length and 600 p in width. In sagittal section, the gland is arranged as follows: the central part is occupied by the reservoir filled with secretory product and limited by a porous cuticle; beneath the cuticle lie numerous canals which are often piled up and interdigitating. The periphery of the gland is occupied by the voluminous secretory cells, resting on a basal lamina; some canals can be seen at this level. Ulrrcrstructurnlstudy The glandular region situated around the reservoir is composed of secretory units which are contiguous and identical. Each of these (Fig. I) consists of two proximal secretory cells lying side by side, each having an excretory channel formed by invagination of the plasma membrane. These two channels unite in the neighbouring
‘95
cell, the intermediary cell, which lies opposite the two proximal cells. As before, this channel is limited by a plasma membrane invagination; the channel lumen is extended by an epicuticular canal which enters the canal cell. The latter is elongated and exhibits secretory characteristics. It surrounds the canal as far as the middle of the cuticle after which point the canal is defined only as an epicuticular invagination into the cuticle. Interspersed with the canal cells are glycogenrich cells, the cytoplasm of which is extensive and ramifying. Study qf’reservoir cuticle The reservoir is limited by a cuticle 6--X p in thickness. The most external region (Fig. 12) is a multilayered epicuticle: the outermost layer is very electron dense and is followed in sequence by an electron-lucent layer, another layer of high electron density thicker than the first, and possibly a second lucent layer. A thin exocuticle appears to be present under the epicuticle and above a thick lamellate endocuticle showing the characteristic ‘parabolic’ appearance. The distal part of the canals is three-layered, the central layer being less dense than the other two (Figs. 13, 14). Study qf’cr secretory wit (a) The two proximal cells (Figs. I --7). These are unusually large (40-50 p in height and cu. 20 p in width) and are always filled with secretory granules. The nucleus (Fig. 4) is generally situated in the basal third of the cell; it is irregularly shaped and possesses finely granular chromatin distributed throughout the matrix and two large, generally peripheral and heterogeneous nucleoli. The cytoplasm is characterized by the grouping of some of its organelles. The proximal part of the cell includes a
Fig. I. Diagram of one glandular unit of the postgonopodial gland; C, centriole; CC, canal cell; Cc,, excretory cdnal of the glandular unit; CG, glycogen cell; CI, intermediarv _ cell: CS. .uroximal secretorv . cell: Cu. cuticle: D, desmosome: /Ii. diolosome; I, granule with rods of dense material; R, reservoir; RG, rough endoplaimic reticulum. ZC, small channel zone; ZG, Golgi zone; ZM, mitochondrial zone.
JUBERTHIE-JUPEAU
region containing little other than abundant cisternae of the endoplasmic reticulum (Fig. 3) which are in places very dilated. Rough ER cisternae are also seen between the secretory granules. In some cells, the contents of the ER cisternae are only slightly electron dense, and in this case the overall appearance of the cell is very clear. Other cells exhibit ER cisternae containing very opaque material, thereby appearing denser than the preceding cell types. The mitochondria (Fig. 3) are, for the most part, grouped in a single zone adjoining the nucleus. Here, they are closely packed in cytoplasm devoid of other components except for occasional vesicles of the rough ER. These mitochondria are small and more or less flexuous and possess sparse narrow cristae. The Gogli complexes (Fig. 4) are grouped into a spherical zone and the externallylocated forming face of each complex frequently shows dilated cisternae. Their activity gives rise to numerous electrondense vesicles that migrate towards the centre of the Golgi zone. Successive aggre-
gation of these vesicles produces subspherical masses, sometimes very heterogeneous, which are probably the origin of the secretory granules. Furthermore, in the centre of some Golgi zones occur secretion droplets resembling those present in other parts of the cytoplasm. The secretory granules (Figs. 2, 3) occupy most of the cytoplasm, and in particular, they are clustered in a fourth area-the small channel zone (Figs. 2, 5). This very specialized area is situated around the excretory channel of the cell. This channel is very short, and divides into small tortuous channels which in turn divide again in a region where the cytoplasm contains many microtubules and filaments and lacks other cell components (Fig. 2). The entire small channel system forms an extracellular cavity. Secretory granules reach the margin of this zone. A centriole is always present at the edge of this area: this presents the usual nine triplets (Fig. 7), however microtubule A in each triplet possesses an extra microtubule on its internal aspect. The two secretory cells of each unit are
Fig. 2. Section through the proximal secretory cells (CS) in the small channel zone (ZC) and through the intermediary cell (CI) of a glandular unit; C, centriole; D, desmosome; S, secretory granule; ZF, fibrillar zone around the central channel (Cp) of the intermediary cell. x 15,000. Fig. 3. Basal part of a proximal secretory cell. MB, basal lamina; S, secretory RG, rough endoplasmic reticulum; ZM, mitochondrial zone. x 18,000.
granule;
Fig. 4. A section of the nucleus (N) and the Golgi zone (ZG) of a proximal cell. S, secretory granule. x 6600.
secretory
Fig. 5. Proximal secretory cell (CS) and intermediary cell (CI). The excretory channel of the secretory cell which is formed by an invagination of the plasma membrane and the small channels are situated in a fibrillar zone called the small channel zone (ZC). A secretory granule (S) largely surrounded by filaments is about to pass into the channel. In the fibrillar zone (ZF) of an intermediary cell is a channel Ct adjoining that of the secretory cell Cx and the perpendicular channel Cp seen in transverse section; D, desmosome. x 32,000. Fig. 6. Secretory x 24,000.
granule(S)
of a proximal
secretory
cell approaching
Fig. 7. Centriole of a proximal secretory cell. Note nine triplets, which are associated with a surnumerary tubule. x 63,000.
a small channel. the A tubules
of
Fig. 8. Intermediary cell showing the two transverse channels (Ct) facing the excretory channel (Cx) of a proximal secretory cell. These two unite to form a perpendicular channel (Cp); D, desmosome; ZF, fibrillar zone. x 43,000.
POSTGONOPODIAL
GLANDS
OF A MYRIAPOD
contiguous except at their contact with the intermediary cell, and are symmetrically placed with respect to the latter. In particular, the small channel zone faces each side of the intermediary cell. (b) The intermediary cell. This small cell is located between the two previously described (Figs. 1, 2, 8). Its membrane is invaginated adjacent to the small channel zone of each secretory cell. Thus two channels are situated in front of the excretory channel of each secretory cell (Fig. 8). The two channels of the intermediary cell unite centrally to produce one perpendicular channel. The latter is cu. 3000 8, in diameter and scarcely 2 p in length and reaches the base of the adjoining canal cell (Fig. 9). lintil it reaches the level of the canal cell, the secretory product of proximal cells is contained only by the plasma membrane of the intermediary cell. The central part of these cells, in effect, is traversed by channels forming an inverted T: it is subspherical and contains only densely packed microtubules and filaments which are interspersed, and surround the channels (Fig. 8). This region of the intermediary cell is linked to the secretory cells by an extremely well-developed desmosome. This is dome-shaped, and in the centre the channels of secretory and intermediary cells anastomose. Adjacent to this desmosomal complex are present septate junctions, beyond which no special junctions are differentiated. Around the fibrillar central part of the cell a narrow zone of cytoplasm is present, except at the level of the nucleus. The latter is extensively lobed, and condensed chromatin is distributed in patches. A diplosome is always present at the margin of the fibrillar zone. (c) The curzal cefl. This cell (Figs. 1, 9-l 1, 14417), the proximal region of which adjoins the intermediary cell and the distal part of which penetrates the cuticular reservoir, exhibits along its entire length a cavity that ensheaths the canal. The wall of the canal can be seen just at the end of the channel of the intermediary cell: this is a tube of electron-lucent homogeneous material which maintains a similar structure up to the epicuticular invagination. Beyond the inter-
299
mediary cell the secretory product passes into the lumen of a true canal which is ca. 4500 A in diameter and is without a bulb. The canal cell shows deep invaginations of the plasma membrane adjoining the entire length of the canal (Figs. 10, 11). These invaginations are wide and more or less cylindrical along almost the entire length and are filled with homogeneous material of low electron density which contains small subparallel rods of much denser material. In the subdistal part of the cell, very deep and flat infoldings surround large mitochondria (Fig. 14). The nature of the canal changes between the regions withand without mitochondria. The homogeneous part of the canal forms a pad beyond which it displays the three-layered epicuticular pattern (Fig. 15): the cytoplasm at this level exhibits several bundles which are perhaps fibrillar and which are bent and arranged in a spoke-like fashion (Fig. 16). The canal cell is enlarged in the basal region where the nucleus is located. Within the cytoplasm, microtubules are oriented along the long axis of the cell and are most numerous in the apical region. In addition, the cytoplasm contains active Golgi complexes, small mitochondria, numerous free ribosomes and short cisternae of the rough ER. The last are sometimes arranged in rings and appear to be engaged in secretion, but the origin of secretory product in invaginated cavities has not been determined. (d) The glycogen cells. These ensheath the canal cells almost throughout their entire length, except at the level of the cuticle. They display a very extensive cytoplasm, dissected into thin flanges that penetrate between canal cells. The nucleus of these cells may be situated at various levels; it is always irregular in shape, and includes chromatin of low electron density in the peripheral nucleoplasm. The cytoplasm contains free ribosomes, some rough ER cisternae, small mitochondria, microtubules and, in particular, large amounts of glycogen dispersed throughout the ceil. Granules of glycogen are frequently clustered in clear areas of cytoplasm (Fig. IO). Release qf’secretory products qfproximul cells The whole area of the small channels proximal secretory cells corresponds
of the to an
JUBERTHIE-JUPEAU
extracellular cavity, as in most other integumentary glands previously described. The secretory granules are released into the small channels: prior to release the granules within the small channel zone are surrounded on all sides by microtubules and many filaments, and come into contact with the surface of a small channel. Fusion of the membrane limiting the secretory granule and that of the small channel takes place (Figs. 5, 6), and the content of the granule passes into the channel. The microtubules and filaments may play a mechanical role in this process. Discussion
In Myriapoda, the fine structure of a pheromone-producing gland, the secretion of which performs a communicative function in mating behaviour, is here studied for the first time. As in all integumentary glands of arthropods, postgonopodial glands of Glomeris
marginata are made up of a large number of
secretory units, joined together. The secretory product of each of these units is released into a common reservoir connected to the exterior via a wide duct. Each glandular unit is partially ensheathed by cells containing glycogen. Each unit consists of two proximal secretory cells, an intermediary cell without secretory characteristics and a canal cell which is secretory in nature. The proximal secretory cells are very uniform in structure and are closely associated; each possesses a small excretory channel formed by imagination of the plasma membrane which ramifies to form an extracellular cavity. Each glandular unit, displaying an exto ‘Class 3’ cretory canal, corresponds epidermal glands as defined by Noirot and Quennedey (1974). Each could originate, as in all dermal glands of insects (Delachambre, 1973) from a gland similar to the type B dermal glands of Rhodnius (LaiFook. 1970) and exhibits a secretory cell
Fig. 9. Section showing the positions of the two proximal secretory cells (CS), of the intermediary cell (Cl) and of the basal part of the canal (CC); Ce, canal filled up with a secretory product; D, desmosome; N, nucleus of intermediary cell; SC, secretory product of the canal cell; ZC. small channel zone. x 17,000. Fig. 10. Transverse section through the canal cell. Ce, canal; of the canal cell; CG, glycogen cell; m, microtubules. x 32,000.
SC, secretory
product
Fig. 11. Transverse x 32,000
SC, secretory
product.
section through
the canal cell. Ce, canal;
Fig. 12. Canal (Ce) opening into the reservoir Cu, cuticle; S, secretory product. x 32,000. Fig. 13. Transverse Fig. 14. Transverse cytoplasmic processes.
(R) of the postgonopodial
section of the canal beneath section through x 28,000.
apical
part
its aperture. of canal
Cu, culicle.
gland. x 32,000
cell. Cu, cuticle;
DC,
Fig. 15. Subapical part of the canal cell (CC) shown facing the invaginations without any mitochondria (Di), the epicuticular structure of the canal and, facing the invaginations with bulky mitochondria (Dm), the homogeneous structure of the canal. x 32,000. Fig. 16. Transverse section of the canal cell between the invaginations with large mitochondria and the invaginations Jacking mitochondria; E, fibrillar bundles around the canal; Cu, cuticle. x 43,000. Fig. 17. Transverse section M, mitochondria. x 43,000.
of the canal
cell at the level of large mitochondria.
PDSTGOhOPODlAL
GLANDS
OF
A MYRIAPOD
10I
0 15
POSTGONOPODlAL
GLANDS
OF A MYRIAPOD
with an extracellular cavity in connection with the lumen of a canal secreted by one or more cells. The extracellular cavity of G. murginatu resembles the branched extracellular chamber of the accessory salivary glands of the Tettigoniid Homovocovyphus uitiddus. The canal of G. marginatrr is secreted by one cell, secretory in nature. Two secretory cells are present, and between them and the canal cell is located an intermediary ceil. As far as cytoplasmic organelles are concerned, the most prominent feature of organization is the great development of microtubules and filaments especially in the small channel zone of the secretory cells, in the central region of the intermediary cell and in the canal cell. A centriole is always present in each secretory cell and a diplosome in the intermediary cell. These are located at
w
the margin of a zone of filaments. The centriole of the proximal secretory cells is unusual: it displays the classical nine triplets pattern but the A tubule is equipped with a supernumerary tubule on its inner face. No direct relationship can be seen between tubules of centrioles and cytoplasmic microtubules; it is only possible to note their proximity and constancy. The release of secretory granules into a small channel occurs when a granule is surrounded by microtubules and filaments and following membrane fusion. i.e. by exocytosis. The proximal secretory cells empty their product into the lumen of the small channels and thence the canal without any filtration, but the secretory product of the canal cell must pass through the canal wall. The two secretory products are blended before reaching the reservoir
JUBERTHIE-JUPEAU
304
References ANSTEE, J. H. 1975. The fine structure of the ‘accessory glands’ of the Tittigoniid, Homorocoryphus niridus. J. Insect Physiol., 21, 1211-1217. DELACHAMBRE,J. 1973. L’ultrastructure des glandes dermiques de Tenebrio molitor L. (Insecta, Coleoptera). Tissue & Cell, 5, 243-257. DEMANGE,J. M. 1959. L’accouplement chez Graphidostreptus tumuliporus (Karsch) avec quelques remarques sur la morphologie des gonopodes et leur fonctionnement. Bull. Sot. eat. Fr., 66, 198-207. HAACKER, U. 1969. Spermaiibertragung von Glomeris (Diplopoda). Naturwissenschaften, 56,467. HAACKER, U. 1970. Der Stridulationsapparat von Loboglomeris und seine Funktion im Sexualverhalten. Vie Milieu (C), 20, 57-64.
HAACKER, U. 1971. Trommelsignale bei Tausendftisslern. Naturwissenschaften, 58, 59-60. HAACKER, U. 1972. Communication in courtship and mating behaviour. Symp. Zool. Sot. London (1974), 32, 317-328. JUBERTHIE-JUPEAU,L. et TABACARLJ,1. 1968. Glandes postgonopodiales des Oniscomorphes (Diplopodes, Myriapodes). Revue Ecol. Biol. Sol, 5 (4), 605-618. KINKEL, H. 1955. Zur Biologie und Okologie des getiipfelten Tausendfusses Blaniulus guttulafus gerv. Z. angew. Eat., 37,401-436. LAI-FOOK, J. 1970. The fine structure of developing type ‘B’ dermal glands in Rhodnius prolixus. Tissue & Cell, 2, 119-138. MAURIES, I. P. 1969. Observation sur la biologie (sexualit&, p&riodomorphose) de Typhloblaniulus lorifer consoranensis BrGlemann. Diplopoda, Blaniulidae. Ann. SpPIPol., 24,495-504. NOIROT, Ch. and QUENNEDEY, A. 1974. Fine structure of Insect epidermal glands. Annu. Rev. Entomol., 19,6l-80. THIERY, J. P. 1967. Mise en evidence des polysaccharides sur coupes fines en microscopic blectronique. J. Microsc., 6, 987-1018.