No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 201 
forms are especially interesting, as E. B. Wilson has remarked 
(3), because in each of them a yolk mass appears after the layers 
have been completely formed. I have not seen Kowalevsky’s 
figures, but the yolk shown in Jourdan’s figure 11g is precisely 
like the yolk of a young Manicina (making allowance for differ- 
ence in thickness of the sections). The @ gréorz improbability 
that the endoderm would first secrete a yolk (Kowalevsky) and 
then swallow it again, taken together with the similarity of the 
yolk in question to that of Manicina, might tempt one to believe 
that both authors had mistaken a stage like Fig. 12, Pl. I., fora 
true gastrula. But Kowalevsky’s statements on this head are 
so definite as to preclude this supposition. 
b. Supporting Lamella. 
The only two authors who have described in detail the forma- 
tion of the supporting lamella are Jourdan (/c.) and Wilson (Z.c.). 
Jourdan’s observations were made on a coral, Balanophyllia, and 
an actinia, Actinia equina. He draws a sharp distinction be- 
tween the ‘membrana propria” and the jelly. 
The former answers to the German Stutzmembran. It isa 
firm limiting membrane which appears between the two layers 
and extends into the mesenteries to form their axial bands. 
This is what I have spoken of as the supporting lamella (comp. 
any of figures on Pl. IV.). Its origin Jourdan was unable to 
trace with any certainty. The jelly, on the other hand, which 
eventually becomes fibrous, is formed outside the membrana 
by the superficial ectoderm cells. The inner ends of these 
cells break off and fuse together to form a granular mass, in 
which fibres subsequently appear (/.c. Figs. 119 and 129). 
The supporting lamella described by Wilson is evidently the 
same thing as Jourdon’s membrana. Its origin according to Wil- 
son is double. In the mesenteries it isa simple cuticular secre- 
tion of the ectoderm cells. But in the body wall it is formed 
in a manner similar to that just described for the jelly: the 
inner ends of the ectoderm cells become swollen, constrict off, 
and form a granular layer which condenses to a smooth mem- 
brane. 
In Manicina there is first formed a very distinct membrane 
as described. In later larval stages, at various spots, especially 
in angles, a thin fluid jelly accumulates. This is noticeable in 
