Growth and the Development of Pattern

t INS - Decemh,'r I ~,~¢2

454 tern is studied in monkeys and man. The role of cerebellar nuclei in different types of ocular movements and in the plasticity of vestibulo-ocular reflex is analysed in the remainder papers. There are a few papers that examine auditory-vestibular interactions showing acoustic-induced eye movements and suppression of vestibular nystagmus by fixation of visual and acoustic targets in patients. Three chapters concentrate on clinical work and cover abnormal head-eye interactions and eye movements in patients with different types of CNS disorders. Dynamic changes in the

vestibulo-ocular reflex and studies of visual-vestibular interactions are studied in the diagnosis of vestibular disease. There is no material on eye muscleper se. The work reported is generally very good and many leading investigators are included among the authors. Most of the information has been. or will be, published elsewhere but it is convenient to find such a wide variety of material gathered in one volume. All papers are relatively short and the majority concentrate on recent experimental work reported in the traditional way (Introduction, Methods, etc.). The abun-

JEEM Supplement on pattern formation Growth and the Development of Pattern

edited by R. M. Gaze, V. French, M. Snow and D. Summerbell, Cambridge University Press, 1981. £21.00 (i + 325 pages) ISBN 0 52l 24557 5 At least three symposia dealing with pattern formation have been published in the last several months: 'Growth and the Development of Pattern (Journal o f Embryology and Experimental Morphology, vol. 65 supplement, 1981 ; JEEM); 'Theories of Pattern Formation' (Philosophical Transactions o f the Royal Society o f London, ser. B, vol. 295, no. 1078, 1981; PTRS); and 'Principles and Problems of Pattern Formation in Animals' (American Zoologist, vol. 22, no. 1, 1982; A Z ) . Their titles reflect their respective emphases rather well. All three cover many topics, but the first gives special attention to the problem of how growth and the ultimate size of a structure are regulated in relation to the structure's pattern, the second emphasizes formulation of theories to account for pattern formation, and the last is an eclectic collection which contains discussions of pattern, growth, theory, and more studies on neural systems than the first two. Neither the mechanism(s) by which patterns are established, nor the mechanism(s) by which growth is regulated, are known in any system. The precision of each, however, can be impressive - for example, insects are sometimes classified into species or even genera on the basis of minute details of bristle number, location and morphology; and the two wings of a single chick embryo are matched in length to within 2% in most individuals (Summerbell, J E E M ) . Some workers (e.g. Holder, J E E M ) feel that there is a direct and obligatory link between pattern and size, whereas others (e.g. Maden, J E E M ) lay more emphasis on cases in which the two can be dissociated. An explicit discussion of panem formation and size regulation is

dance of detailed observations does not bring an easily assimilated overview of the fields for the non-specialist. Unfortunately. there is no summary on major points of consensus or conlroversy and the volume does not reflect the modifications of the points of view which may have resulted from discussions between this outstanding international group ~f contributors. S. T'~(-f)UMONT

Unite de Recherches Neurobiologiques. INSERM

U-6, 280 Bird Sainte-Marguerite. 13000 Marseille, France.

development fit models of this kind? Anderson (JEEM) gives a lucid account of central projections from sensory neurons given by Cooke (AZ). developing at ectopic sites in several differMost of the papers in all three symposia ent insect systems, with the conclusion that make use of the concept of 'positional the developmental history of a sensory cell information'. This term was introduced matters but its (ectopic) location does not almost 15 years ago by Wolpert to encapsu- the new positional information, if it indeed late the idea that a cell differentiates on the exists, does not exert an effect on the cell's basis of two distinct factors: its genetic con- projection in the CNS. Other authors make stitution and developmental history on the greater or lesser use of the positional inforone hand, and the location in which it finds mation framework. Morris-Kay (JEEM) itself on the other. In this model cells from discusses the morphogenesis of the cranial the toe-to-be region of the foot grafted to the neural epithelium during neurulation in elbow-to-he region of the ann would dif- rats. Diamond (AZ) reviews the distribuferentiate into knee structures; they would tion and behaviour of peripheral sensory maintain their hindlimb identity, but they endings in vertebrate skin. Summerbell and would form structures according to their Stifling (AZ) describe the development of new position in the forelimb. The co- the innervation of chick limbs. Finally, ordinate systems which convey information Hunt et al. ( A Z ) describe some ambitious about location are believed to be common at studies on eye development in amphibians. least to all the appendages of an individual This last paper raises, in a neurobiologi(hence leg cells can read ann positional cat context, the issue of compartments. information), among individuals of a These are regions, best known in insect species, and across related species. In fact, bodies, which have boundaries across they might be universal, at least among which cell migration does not occur so that animals (e.g. Summerbell, A Z ) . discrete cell populations are established. Many questions can he asked about posi- Ideas about the origin and significance of tional information. Is it conveyed to cells compartments are discussed by Karlsson by some diffusible material(s) with mor- (JEEM), Kauffman (PTRS), Lawrence phogenetic effects (Gierer, PTRS; McWil- and Wright (PTRS), French (,4 Z), Morata liams. A Z ) ? Is the co-ordinate system a (AZ), Meinhardt ( A Z ) and, in a mampolar rather than a Cartesian one (Holder, malian context, by Snow (JEEM). The J E E M ; French, PTRS; several authors in related and perhaps more general problem A Z ) ? Are there electrical currents whose of segmentation is discussed by Cooke distribution gives a positional information (PTRS and A Z ) . Lawrence and Wright (Jaffe, PTRS)? Could positional informa- (PTRS), Schubiger and Newman (AZ) tion be a matter of history, given by the time and French (AZ). which a cell spends in a critical zone before It would be impossible to summarize, let its place there is taken by another cell alone evaluate, the papers in even one of (Wolpert, PTRS ) ? these symposia. Taken together, however, Positional information is believed to he they convey a sense of the dynamism which interpreted by cells, with differentiation pervades the field of pattern formation, the being the outcome of this interpretation. A difficulties with general concepts like posinumber of authors consider the possible tional information or the polar co-ordinate role of cell lineage in the interpretation model, and the never-ending string of surprocess (Simpson, J E E M ; Snow, J E E M ; prises from new experiments. Kauffman, PTRS ; Kimble, PTRS ; J. PALKA Morata, A Z: Hunt, et al.. A Z; Meinhardt, AZ), Department of Zoology, Universityof Washington. To what extent do data on neural Seattle, WA 98195, U.S.A