200 WILSON. [Vot. Il. 
i.e, none of the blastosphere cells migrate into the interior, but 
the endoderm is formed exclusively by delamination. 
Though the way in which the solid larva was originally 
formed seems preserved in but a few species, the solid larva 
itself may fairly be considered as typical for the Ccelenterates. 
It is especially well preserved in the Hydroids and Anthozoa. 
In the latter group it is nearly universal among Alcyonarians, 
and occurs in the majority of the Zoantheria. The Alcyonarian 
which comes nearest to J/anzcina in the formation of its layers 
is Renilla (3). In this genus, though the blastosphere has a very 
small cavity, the endoderm is formed by delamination, as in the 
coral. As regards the structure of its larval endoderm, how- 
ever, Renilla differs from Manicina. In the former the endo- 
derm is made up of a mass of cells, of which the peripheral layer 
becomes the permanent endoderm, while the central cells go to 
pieces, and are probably eaten, amoeboid fashion, by the periph- 
eral cells. In Manicina, on the other hand, the larval endoderm 
is a plasmodium, and in the entire process which leads up to the 
formation of the adult endoderm it would seem that a prominent 
physiological part is played by the “ vesicles,’ which in all proba- 
bility contain some kind of yolk. Owing to the plasmodial nature 
of the solid endoderm, the complete transformation of the latter 
into the permanent layer must require less time in Manicina than 
in Renilla. For in Manicina there is no large accumulation of 
yolk cells which must slowly be devoured, amoeba fashion, by the 
peripheral cells. On the contrary, when the time for the forma- 
tion of the permanent endoderm has arrived, the general proto- 
plasm is merely drawn towards the periphery, and after it has 
there broken up into cells, there remains but little nutriment 
in the loose yolk mass. Just how the yolk is ingested after the 
cellular endoderm is formed, Iam unable to say. It is not de- 
voured, amoeba fashion, by the endoderm cells at large, though 
in the region of the cesophagus, Figs. 6 and 8, connection is 
maintained for a considerable time between the yolk and the 
endoderm, which elsewhere is completely formed. 
Amongst the corals and actinias, two or three forms have 
been described as undergoing invagination, notably Cerzanthus 
(Kowalevsky 4) and Actznza (Jourdan 5). While the mere recur- 
rence of invagination in a ccelenterate group can scarcely be 
said any longer to have a phylogenetic significance, these two 
