rise of fish embryology in the nineteenth century, The

American Zoologist, Jun 1997 by Wourms, John P

Considering its promising beginning, it is surprising that the study of chondrichthyan development made relatively little progress in the eighteenth century. There are many possible reasons. Those scholars interested in fish biology may have been attracted to systematic studies because of the revolutionary efforts of Willughby and Ray, Artedi (1705-1735), and Linnaeus (17071778) as well as the influx of new species of fishes from the tropics. Changing fashions in science also enter the picture, especially the rise of microscopy and microscopic anatomy. Perhaps in terms of the material, questions, and technology, research on chondrichthyans had reached an impasse. There are some exceptions. Bohadsch (1776) investigated the structural organization of eggcases. Monro (1785) published detailed descriptions accompanied by elegant illustrations of the urogenital anatomy of the oviparous skates. He also described and illustrated for the first time the spermocysts, spherical aggregations of Sertoli cells and differentiating sperm cells that are a characteristic feature of chondrichthyan spermatogenesis. Descriptions and illustrations of microdissections of the internal anatomy of mid- and late-stage embryos are given. The extensive vitelline circulation and the connection of the yolk sac and the small intestine are documented. External gill filaments, another feature of chondrichthyan development, are described for the first time. The eighteenth century concluded with Bloch's magnum opus (1782-95) which added little to the study of chondrichthyan development other than information on the embryos of the viviparous sawfish Pristis.

The study of teleostean development, as previously noted, lagged well behind that of both oviparous and viviparous chondrichthyan fishes, and little was done prior to the mid-late eighteenth century. To be more accurate, the little that was done was done with viviparous teleosts. Schoenveld (1624) first described viviparity in the embryos of the eelpout, Zoarces viviparus, a fish common to the marine waters of northern Europe. Late stage embryos are illustrated. Impressed by the substantial growth of the embryos during gestation, Schoenveld postulated that they obtain nutrients by ingesting ovarian fluid. (In viviparous teleosts, an oviduct or uterus is absent and gestation takes place in the ovary. Cf. Wourms, et al., 1988). Somewhat later, Willughby and Ray (1686) apparently observed the development of live Zoarces embryos. Interest in teleost development during the seventeenth and eighteenth centuries seems to have been generated by the viviparity of exotic species discovered during the explorations of the Old and New World Tropics. Anableps, the four-eyed fish, conspicuous because of its size, unusual anatomy, and behavior in its Central and South American habitats, was described as viviparous as early as 1738 (Artedi, 1738). Gronovius (1754-1756) was the first to illustrate advanced embryos of Anableps with their characteristic rugose "yolk sac" (actually the abdominal trophoderm). Gronovius may also have been the first to describe viviparity in the clinid, Clinus superciliosus. Bloch (1782-1795) described and illustrated the external and internal reproductive anatomy of Anableps, its embryos in situ, and the embryos themselves. He also depicted the adults and embryos of Zoarces and Clinus. One of the first sets of field observations was made by de Alzate y Ramyrez in 1769 (cited in Gill, 1882) who discovered viviparity in a Mexican poeciliid and made microscopic observations of blood circulation in living, near-term embryos.