34 Mr. H. J. Carter on the Ovigerous Layer of 
upper half of the Zurritella on which the sponge had grown 
remains with the ovigerous layer still on it, while the lower part 
has disappeared and left not a trace of ova or the ovigerous 
layer behind, where both originally existed (fig. 1), and in 
another, where the original shell has passed away and a 
smaller one has been enclosed, apparently for the purpose of 
receiving a new ovigerous layer), it seems not impossible that 
impregnation and the further development of the ovum may 
take place with the disappearance of the shell, when the embryo 
at least could easily escape through that part of the capsule 
which was in contact with it, and which I have stated to be so 
extremely thin (fig. 2, d). 
Let us now turn our attention for a few moments to the ova 
of other marine sponges, to see how far they agree with those 
of Suberttes domuncula ; and selecting Lsodictya simulans, Bk., 
for this purpose out of several ova-bearing ones that I have, 
preserved in spirit, the ova will be found to be congregated 
in the sponge towards the base or oldest part, but not attached 
to the rock on which the sponge may have grown, as in 
uberites domuncula. While thus isolated they present a sphe- 
rical form so long as the yelk has not passed into the fully 
developed embryo; but when this is completed the embryo 
bursts through the delicate capsule which enclosed it, and then 
assumes the form of a conical shot or elongated cone with a 
little tuft at the obtuse end (the long cilia). Under the former 
or spherical condition, in my specimen, the grumous or clotted 
state of the contents and presence of spicules already show 
that the originally granular state of the yelk has been trans- 
formed through duplicate subdivision with its consequences, 
into the coming embryo, and thus the presence of starch, 
although evident under the use of iodine, is now very trifling, 
showing that in the egg of the Suberite, as in the seed of 
plants, it is abundant at the commencement and disappears 
in the usual way under germination. 
The same observations apply to the ova of Halisarca lobu- 
laris, Aplysina corneostellata (Darwinella aurea), Esperia, and 
Halichondria sanguinea, Johnst., so that we here see the 
animal nature evinced in spite of the resemblance of the ova 
of sponges to the seed of plants ; for while the sponge-embryo 
develops a root for fixation only, and a superstructure tor 
supporting organisms that take in crude material for food, that 
of plants develops a root for nutrition as well as fixation 
and a leafy superstructure, viz. the “ plumule,” which grows 
by endosmosis through the spongioles at the ends of the 
radicles. 
Having already gone into the subject of impregnation in 
