202 WILSON. [VoL. II. 
Figs. 16 and 17, beneath the right-hand mesenteric filament, 
and in Figs. 44 and 45 at the angles of the cesophagus. It is 
always to be found in the axis of the larval filament, Fig. 26. 
The distinction between the supporting membrane and the 
more fluid jelly, which is noticeable in larval stages, is lost later 
in life. In the older larve, Fig. 39 for instance, the supporting 
membrane throughout its whole extent has become consider- 
ably thicker than in younger stages, though the jelly in the axis 
of the filament is still to be distinguished from the more mem- 
brane-like band of the mesentery. In the adult the axial band 
of the mesentery is so much wider, while the jelly in the axis 
of the filament is at the same time denser than in larval stages, 
that all distinction between the two structures is lost. Com- 
pared with an actinia the whole mesodermic skeleton of the 
adult Manicina is very scanty and membrane-like, but in certain 
places it reaches a more generous jelly-like condition, for exam- 
ple, in parts of the mesenteries, Fig. 51. Here the supporting 
substance is merely the thickened primitive membrane. 
There indeed seems to be no difference between the support- 
ing membrane proper and the jelly, except in the mere quantity 
of the secreted substance and in the percentage of water. What 
applies to the origin of one should explain the origin of the other. 
Now as regards the membrane proper, I am quite sure that in 
Manicina it is formed as a cuticular secretion, and not by the 
direct conversion of the ends of ectoderm cells into granular 
matter, which subsequently condenses to a membrane. Turn- 
ing now to the question as to which layer secretes the membrane, 
we see from the figures (14, 17, 26, 45) that after the mesenteries 
are formed, the lamella is much more intimately connected with 
the endoderm than with the ectoderm: where the layers are 
forced apart, it always sticks to the endoderm. But even here 
the ectoderm is provided with a well-defined limiting membrane, 
which if thinner than the lamella, is essentially like it. I con- 
clude from this and other facts to follow that when the lamella 
lies between the two layers, both layers share in secreting it. 
That the endoderm cells can secrete the lamella, is plain from | 
its occurrence in the axis of the mesenteries, and in the axis of 
the genital bands of a Cubomedusa (6). On the other hand, the 
same argument can be used to prove the ability of the ectodermal 
cells to secrete this substance, for in the velum of Hydromedu- 
