The development of Renilla
Edmund Beecher Wilson · 1882
THE observations recorded in the following pages were made in the course of three summers' work at the marine laboratory of the Johns Hopkins University, organised and directed by Professor W. K. Brooks, and located for the past three years at Beaufort, N.C., where the material for this paper was collected.The abundance of Renilla reniformis (Cuv.), at Beaufort, suggested the desirability of a careful study of its embryology, and this was rendered still more apparent by the studies which Mr. Mitsukuri had made upon the anatomy of the adult organism.I was therefore much pleased when a lucky accident, during the summer of 1880, put me in possession of a few very young colonies.Subsequent search over the ground resulted in the discovery of a considerable number of young colonies in various stages of growth, and I was thus enabled to make a rather full study of the growth of the colony from the simple primary or axial polyp up to the adult organism with its secondary polyps in a state of full sexual maturity.A single specimen, finally, of the ciliated larva was taken at the surface and kept in the aquarium until the free-swimming life was abandoned and the characteristic tentacles and spicules made their appearance.An outline of the general results of these observations was published in the American Journal of Science for December, 1880, a full description being however deferred in the hope of procuring still earlier stages for a study of the embryonic development.This hope was happily realised in the following summer, when two or three lots of fertilised eggs were obtained; and, finally, in the season of 1882, the eggs were procured in considerable abundance, and a very satisfactory study of the phenomena of development was effected.During the latter season the eggs of a Gorgonian, Leptogorgia virgulata (Epw.and Hare), were procured-though in small numbers only-and I have studied to some extent the development of this polyp also.The material was however scanty, and the development, so far as observed, closely similar to that of Renilla; hence these obser-724 DR.E. B. WILSON ON THE DEVELOPMENT OF RENILLA.vations will be described only for the sake of comparison and in connexion with those relating to Renilla, I have been unable to overcome entirely certain technical difficulties, and my results will therefore be found inconclusive on a few points.Furthermore, the unexpected close of the spawning period during the last season's work brought to an unwelcome close my observations on the earlier stages of development, and I have not been able, for this reason, to follow in detail the phenomena of the fertilisation of the egg and the behaviour of the segmentation-nuclei during the early stages.Still I venture to hope that my observations form a decided advance on what is now known of the development of the Alcyonaria.KowAatnyvsky's well-known observations on Sympodium, Clavularia, Alcyonium, and Gorgonia form the basis of almost the whole of our knowledge of the subject; and these observations, though of great interest, were published in a very condensed form, and were in part rendered inaccessible to many zoologists through their publication in the Russian language.They indicated that the early stages of Aleyonarian polyps would well repay more extended observation, and this expectation has perhaps been realised in the case of Renilla.So far as the Pennatulacea are concerned, nothing is known of the embryonic development, and only the most meagre accounts exist concerning the mode of budding and formation of the colony.The latter phenomena however involve questions of much interest on account of the highly specialised nature of the colony as expressed in the marked polymorphism of its members and in the remarkable relations of symmetry existing between them.For the foregoing reasons it seems to me desirable to publish these observations without further delay.since I can see in the future no near opportunity of making them complete.Before considering the phenomena of development it will be useful to glance for a moment at some of the structural features of the adult Renilla and their relation to the characteristics of other Alcyonaria.For a full description the reader is referred to the well-known papers of K6LLIKER* and Eisen,t who have described in some detail the structure of Renilla reniformis and R. amethystina.Renilla is a genus of Pennatulacea, a group which forms the highest division of the Order Alcyonaria.The organism, when adult, is a community or colony, the members of which consist of an axial polyp and a large number of secondary polyps produced by the budding of the axial or primary individual and organically united with it.The colony has the form of a reniform dise with a deep sinus at one side into which is inserted a flexible peduncle which roots the organism in the sand.The polyps are arranged in radiating lines over the surface, projecting upwards over the general * " Anatomisch-Systematische Beschreibung der Aleyonarien, Erste Abtheilung, Die Pennatuliden."Abdruck a. d.AbbandJungen d.Senkenb.Naturforsch.