Embryonic Development of the Turkey Male Genitalia

Embryonic Development of the Turkey Male Genitalia MURRAY R. BAKST and HELENE C. CECIL USDA, ARS, Avian Physiology Laboratory, Beltsville, Maryland 2O705 (Received for publication December 23, 1985)

1986 Poultry Science65:1623-1630 INTRODUCTION Recently we described the gross (Bakst and Cecil, 1983) and microscopic (Knight et al., 1984) anatomy of the male turkey cloaca. It was noted that the gross appearance of the Phallus nonprotrudens of a turkey differed from that of a male chicken due to the absence of the Corpus phallicum medianum and the presence of a more prominent Corpora phallica laterale. Contrary to our observations, Burrows and Quinn (1937) described paired Corpora phallica mediale on the Phallus nonprotrudens of the mature turkey. An examination of the external genitalia during embryonic development should resolve the issue regarding the presence or absence of the Corpora phallica mediale in the male turkey. Therefore, the objective of this study was to describe the embryonic development of the male turkey external genitalia. MATERIALS AND METHODS Eggs collected from Diamond Hybrid Large and Medium White turkeys maintained on our breeder farm were incubated under standard commercial conditions. Beginning at 7 days of incubation and daily thereafter until hatch, embryos were removed from eggs, cleaned of extraembryonic membranes, and washed briefly in Hank's buffered salt solution prior to excision of the cloaca. Starting at 8 days of incubation, embryos were sexed based on gonad identification. Cloacae were fixed in 2%

glutaraldehyde/4% formaldehyde (made from paraformaldehyde) in .15 M cacodylate buffer and refrigerated for up to 3 weeks prior to further processing. Fixed cloacae were dehydrated in ethanol and critical-point dried. For scanning electron microscopy, critical-point dried specimens were coated with gold/palladium and examined with an Hitachi-430 Scanning Electron Microscope operated at 15 kV. Sixteen or more male embryos were examined on each day of incubation. Nomenclature used in this study followed the recommendations suggested in Nomina Anatomica Avium (Baumel, 1979). RESULTS Table 1 summarizes the development of the major structures forming the external genitalia and proctodeum. Day 7. Located along the midline cranial to the tail fold is the rounded, knob-like genital (g.) eminence. A raised caudal extension of the g. eminence, the g. crest, joins the tail fold medial to a pair of lateral g. swellings (Figs. 1, 2). Day 8. The g. eminence has transformed into a g. tubercle. A medial groove (Sulcus phalli) forms along the dorsal surface of the g. tubercle and continues caudally along the g. crest (visible only when the g. swellings are removed). The g. swellings are larger and in closer apposition creating the first suggestion of the proctodeal cavity (Fig. 3). The latter is bounded

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ABSTRACT Embryonic development of male turkey genitalia was examined to define more clearly the origin of the structures comprising the Phallus nonprotrudens. At Day 7 of incubation, the knob-like genital (g.) eminence became evident just cranial to the tail fold. A raised caudal extension of the g. eminence, the g. crest, joined the tail fold medial to the paired g. swellings. Between Days 8 and 12 of incubation, the g. eminence differentiated into the g. tubercle (which by Day 18 formed the Phallus nonprotrudens), and the g. crest formed the ventral floor of the proctodeum. By Days 10 to 11 of incubation, the g. swellings had become confluent with the lateral extensions originating from the base of the g. tubercule forming both a collar-like structure around the vent and the dorsal wall of the proctodeum. By Day 23 of incubation, the urodeum and proctodeum had become patent and the overall anatomy of the genitalia resembled that of an immature male poult. (Key words: turkey, cloaca, phallus, genitals, embryo)

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BAKST AND CECIL TABLE 1. Summary of major structures forming the external genitalia and proctodeum derived from the genital eminence, genital crest, and genital swellings

Days incubation

Genital eminence

Genital crest

Genital swellings

Day 8 Days 10-11 Day 18 Day 19

Genital tubercle Ventral wall of the vent Phallus nonprotrudens Dorsal lip of cloaca

Floor of the proctodeum Uroproctodeal fold

Dorsal wall of the proctodeum

Days 15 to 18. Other than the vent assuming a more triangular appearance, the external appearance of the cloaca remains unchanged (Fig. 9). Further differentiation is limited primarily to the ventral floor of the proctodeum. On Day 15, a dimple-like depression is evident on the cranial end of the Sulcus phalli.

By Day 17, two or more grooves are present at this cranial depression that is the future opening to the urodeum. Also on Day 17, a transverse groove is observed around the midpoint of the Sulcus phalli, thus dividing the ventral floor of the proctodeum into cranial and caudal regions. The more caudal region, which retains the Sulcus phalli, is henceforth referred to as the Phallus nonprotrudens. The Phallus nonprotrudens consists of the paired Corpora phallica lateralia (phallus), which extend caudomedially between and beyond the walls forming the vent, and the paired Plicae lymphaticae (lymph folds), which are cranial extensions of the phallus. The two lateral parts of the cranial region of the proctodeal floor have fully or partially merged by Day 18 to form the uroproctodeal fold (Fig. 10). However, communication between the proctodeum and urodeum is not complete until Days 22 to 23. (In contrast, the urodeum remains separated from the coprodeum until Day 27.) Internally, the dorsal wall of the proctodeum is characterized by folds oriented in a craniocaudal direction. Days 19 to 23. The external cloaca becomes more ovoid, and left and right commissures delineate the walls of the vent into the Labium venti dorsale (dorsal lip) and Labium venti ventrale (ventral lip) (Fig. 11). Radially oriented folds (Pars rugosa), first observed on the periphery of the dorsal and ventral lips, extend to the base of the Phallus nonprotrudens by Day 23 (Figs. 11, 12, 13). The inner margins of the dorsal and ventral lips remain smooth and constitute the Pars plana (Figs. 14, 16). The base of the Phallus nonprotrudens thickens and elevates the Phallus nonprotrudens, occluding the vent (Figs. 13, 15). This base forms secondary cuff-like folds under each external protrusion of the Phallus nonprotrudens. The cuff-like folds are continuous with the inner aspect of the ventral lip, lateral aspects of the

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dorsally by the g. swellings and ventrally by the g. tubercle. Day 9. The g. tubercle is rounder and smoother relative to its appearance on the seventh and eighth days of incubation. The g. swellings continue to enlarge and approach each other medially. The base of the g. tubercle extends laterally, becomes more pronounced, and merges with the lateral portion of the g. swellings (Fig. 4). Days 10 to 14. During Days 10 to 11, theg. swellings in close apposition gradually fuse medially in a cranio-caudal direction obliterating the furrow between the two structures (Fig. 5). By Day 11, evidence of individual g. swellings is lost (Fig. 6). Lateral swellings originating from the base of the g. tubercle increase in size and merge more completely with lateral aspects of the g. swellings. The collar-like structure thus formed envelops the g. tubercle creating both the external opening of the cloaca, the Ventus (vent), and the proctodeum, the caudal compartment of the cloaca. The vent assumes an elliptical rather than a rounded configuration and is almost completely occupied by the g. tubercle. The base of the g. tubercle remains associated with the ventral wall of the vent, while the free margin of the g. tubercle remains in close apposition to the dorsal wall of the proctodeum until Day 14, when the space widens (Fig. 7). Internally, the cranial juncture of the dorsal wall of the proctodeum and the ventral floor of the proctodeum (derived from the g. crest) is the site of the opening to the bursa of Fabricius that is patent by Day 14 (Fig. 8).

Ventral lip of cloaca

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Downloaded from http://ps.oxfordjournals.org/ at University of Michigan on June 25, 2015 All figures have been arranged with the tail toward the top of the page and all figure bar-markers represent 500 Mm. FIG. 1. Day 7. Cranial to the tail fold is the genital (g.) eminence (arrowhead). The slight bulges on the base of the tail fold are the paired g. swellings (arrows). FIG. 2. Day 7. Extending caudal from the g. eminence to the tail fold is the g. crest (arrow). FIG. 3. Day 8. Differentiation of the g. eminence into a g. tubercle occurs. The Sulcus phalli (arrowhead) is observed on the caudal face of the g. tubercle. Together the paired g. swellings (arrows) and the g. tubercle form a urogenital sinus. FIG. 4. Day 9. The paired g. swellings have merged with the base of the g. tubercle (arrowheads) which has extended laterally.

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All figures have been arranged with the tail toward the top of the page and all figure bar-markers represent 500 AimFIG. 5. Day 10. The medial furrow (arrow) created by the paired g. swellings are fused and evidence of its presence is lost by Day 11. FIG. 6. Day 11. A collar-like structure now envelops the g. tubercle and the proctodeum, the most caudal compartment of the cloaca. FIG. 7. Day 14. The space between the free margin of the g. tubercle and the dorsal wall of the proctodeum (arrows) has widened. The external cloaca retains this appearance until about Day 18. FIG. 8. Day 14. Removal of the dorsal wall of the proctodeum reveals the ventral floor of the proctodeum. The Sulcus phalli (arrowhead) divides the floor into left and right halves. The opening (arrow) to the bursa of Fabricius (B) is located at the juncture of the dorsal wall and ventral floor of the proctodeum. The duct connecting the proctodeum to the bursa is patent.

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All figures have been arranged with the tail toward the top of the page and all figure bar-markers represent 500 Mm. FIG. 9. Day 18. Except for an increase in size, the external appearance of the cloaca is essentially the same as that observed on Day 14 (Fig. 7). FIG. 10. Day 18. Exposing the ventral floor of the proctodeum reveals that the two lateral parts of the cranial region of the proctodeal floor have merged, thereby creating the uroproctodeal fold (UF). The two transverse grooves (arrows) on either side of the uroproctodeal fold communicate with the urodeum by Day 23. FIG. 11. Day 19. The left and right commissures (arrows) separate the dorsal and ventral lips. Radially oriented folds (Pars rugosa) (arrowheads) appear at the outer margins of the dorsal and ventral lips. FIG. 12. Day 20. The Pars rugosa are more pronounced. Immediately subjacent to the phallus are smooth folds (Pars plana) (arrows) which follow the contour of the phallus. DISCUSSION floor of t h e p r o c t o d e u m , and t h e u r o p r o c t o d e a l At n o time during e m b r y o n i c d e v e l o p m e n t fold (Figs. 13 to 16). Days 24 to 21. T h e cloaca assumes an are structures h o m o l o g o u s to t h e male chicken medianum or t h e t u r k e y a p p e a r a n c e similar t o t h a t of a poult. T h e Corpus phallicum Corpora pballica mediale (Burrows and Quinn, dorsal lip p r o t r u d e s over t h e phallus (Fig. 17), and all exposed surfaces of t h e "resting cloaca" 1937) observed. Therefore, it is confirmed t h a t consists of are characterized b y t h e radial folds of t h e Pars t h e t u r k e y Phallus nonprotrudens rugosa. R e m o v a l of t h e dorsal lip and dorsal t h e paired Corpora phallica lateralia and the as suggested b y King ( 1 9 8 1 ) , wall of t h e p r o c t o d e u m exposes t h e phallus and Plicae lymphaticae t h e deep c o m p l e x infoldings of t h e Pars plana Bakst and Cecil ( 1 9 8 3 ) , and Knight et al. region of t h e ventral lip lateral t o t h e phallus ( 1 9 8 4 ) . T h e e m b r y o n i c d e v e l o p m e n t of the chicken Phallus nonprotrudens differs from (Fig. 18).

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•

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t h a t of the t u r k e y primarily by t h e r e t e n t i o n of t h e g. tubercle, which develops into t h e Corpus phallicum medianum, and the absence of developed Corpora phallicum laterale and Plica lymphaticae (unpublished observations). R o m a n o f f ' s ( 1 9 6 0 ) comprehensive description of the d e v e l o p m e n t of t h e avian cloaca and

external genitalia illustrates a general p a t t e r n of d e v e l o p m e n t c o m m o n t o m o s t birds including the turkey. Briefly, in t h e turkey e m b r y o after 7 days of incubation, t h e g. e m i n e n c e is observed just cranial t o the tail fold. T h e g. e m i n e n c e soon differentiates into the g. tubercle, which, along with t h e m o r e caudal g.

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All figures have been arranged with the tail toward the top of the page and all figure bar-markers represent 500 Aim. FIG. 13. Day 22. The Pars rugosa are the prominent distinguishing feature of the dorsal and ventral lips. The base of the phallus has thickened and elevated the phallus thereby closing the vent. Subjacent to and following the contours of the phallus are smooth folds (arrows) that continue into the cloaca and form the Pars planar region of the ventral lip. FIG. 14. Day 22. Removal of the dorsal lip and dorsal wall of the proctodeum exposes the floor of the proctodeum. The Pars plana region of the ventral lip circumscribes the proctodeum (arrows) and merges with the uroproctodeal fold (UF). FIGS. 15 and 16. Day 23. The left and right commissures are shown externally (Fig. 15) and internally (Fig. 16) (arrowheads). The fold subjacent to the phallus appears to form a cuff around the phallus and more cranially around the lymph folds (arrow) (uf, uroproctodeal fold).

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swellings, probably constitute the anterior and posterior lips described by Romanoff (1960). The base of the g. tubercle extends laterally to merge with the g. swellings, forming the vent externally and the proctodeum internally, and establishing the fundamental structure of the cloaca and external genitalia. Although not the object of this study, we did note that the Phallus nonprotrudens tended to be larger in male than in female embryos.

ACKNOWLEDGMENTS We thank Anne Kimrey and Noretta Chaney for the expert technical assistance. REFERENCES Bakst, M. R., and H. C. Cecil, 1983. Gross appearance of turkey cloacae after single or multiple manual semen collections. Poultry Sci. 62:683—689. Baumel, J. J., 1979. Nomina Anatomica Avium. Academic Press, New York, NY.

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All figures have been arranged with the tail toward the top of the page and all figure bar-markers represent 500 Mm. FIG. 17. Day 26. A parasagittal view of the cloaca showing the dorsal wall of the proctodeum (1), dorsal (2) and ventral (3) lips of the cloaca, uroproctodeal fold (4), and folds (5, 6) leading from the proctodeum (7) to the urodeum (8). The duct to the bursa (9) and the coprodeum (10) are also present. FIG. 18. Day 25. The dorsal wall of the proctodeum has been removed, but the dorsal lip (DL) remains. The Pars plana region of the dorsal lip (arrows) is continuous with the uroproctodeal fold (between arrowheads). Cranial to the phallus (P) are the two transverse openings (arrowheads) leading to the urodeum. The duct to the bursa (B) is characterized by longitudinal folds.

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Burrows, W. H., and J. P. Quinn, 1937. The collection of spermatozoa from the domestic fowl and turkey. Poultry Sci. 16:19-24. King, A. S., 1981. Phallus. Pages 107-147 in Form and Function in Birds. Vol. 2. A. S. King and J. McLelland, ed. Academic Press, New York, NY.

Knight, C. E., M. R. Bakst, and H. C. Cecil, 1984. Anatomy of the Corpus vasculare paracloacale of the male turkey. Poultry Sci. 63:1883-1891. Romanoff, A. L., 1960, The Avian EmbryO:Structural and Functional Development. The Macmillan Company, New York, NY.

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