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. Kowalevsky’s well-known observations on Sympo- 
dium, 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 manv 
zoologists through their publication in the Russian language. They indicated that 
the early stages of Alcyonarian 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 bud¬ 
ding and formation of the colony. The latter phenomena howmver 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 betwmen 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 Kolliker* and Eisen,! 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 disc 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-System atische Beschreibung der Alcyonarien, Erste Abtbeilung, Die Pennatuliden. 
Abdruck a. d. Abb and! ungen d. Senbenb. Naturforseh. Gesellschaft, Bd. vii., viii. Frankfort, 1872. 
t “ Bidrag til Kannedom om Renilla.'” Kongl. Svensk. Vet. Handl., Bd. xiii. 
