DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
755 
The phenomena of the yolk-absorption have not been carefully studied, and it is 
therefore impossible to draw any general conclusions in regard to the significance of 
the processes described for Renilla. An examination of Jourdan’s descriptions and 
figures of the larvse of Balanophyllia regia (Gosse) leaves in my mind little doubt that 
in this case also the yolk is ingested Amce6<x-fashion by the entoderm cells, though 
Jourdan himself puts an entirely different interpretation on his own observations, as 
may be seen from the following extracts. He says of the entoderm cells at an early 
stage ( l.c., p. 134) : “ Elies sont trhs volumineuses, allongees, contiennent des nucleoles 
fortement colores par les reactifs et de grandes vesicules hyalines. An centre de la 
masse vitelline constituant l’endoderme, ces cellules disparaissent, les vesicules hyalines 
persistent seules” (the italics are my own). In later stages, when six or more septa 
have appeared: “ Sur les coupes transversales, les grandes cellules situ^es au bord 
exteme de i’entoderme des larves vermiformes ont disparu; les vesicules hyalines 
persistent et forment la totality de la masse entodermique.” In later stages, however, 
when the yolk is absorbed, as shown by his figure of the adult entoderm (l.c., fig. 
110, plate 15), the cells come into view again, having the same form as before, but 
rarely containing the “ vesicules hyalines. ” 
It appears in the highest degree improbable that the entoderm cells should 
completely disappear to be subsequently re-developed in precisely the same form. A 
far more credible conclusion is that the yolk-vesicles are taken bodily into the cells 
in such numbers as finally to obscure the cell-outlines entirely. The entoderm then 
seems to have disappeared and only makes its re-appearance when the yolk-vesicles 
have been assimilated by the protoplasm of the cells. This conclusion is strengthened 
by the fact that in Jourdan’s figure of the larva of Actinia equina (l.c., fig. 119, 
plate 16) the entoderm cells are figured, before the absorption of the yolk has begun, 
as clear, well defined, and destitute of yolk-vesicles, while the gastric cavity is 
completely filled with “ vesicules hyalines ” precisely like those of Balanophyllia. 
This condition, according to my view, precedes one like the earlier stage of Balano¬ 
phyllia in which absorption has recently begun and in which the entoderm cells 
resemble those of Astcicus, as figured by Reichenbach.* 
In all known Alcyonarians the central mass, though at first unsegmented, does 
sooner or later divide into cells, although many of these perform no active function, 
become disorganised, and serve only as food for other cells. This indicates that the 
yolk-cells are the descendants of cells which were once of structural significance ; 
for otherwise their formation and subsequent disintegration would seem to be a sheer 
waste of energy. They are identical in origin and structure with the permanent 
entoderm cells, and are undoubtedly homologous with the latter. Hence we may infer 
that the yolk-cells were originally functional entoderm cells in which deutoplasm 
accumulated to such an extent that they became devoted solely to the storing 
of food for the embryo. The remaining entoderm cells retained their functional 
* Zeitschr. fur Wiss. Zool., Bd. xxix., 1877. 
