312 WILSON. EVors EX: 
The formative cells in the recently attached sponge tend to 
break up into solid masses of much smaller cells. Such 
masses are common, several of them being shown in Fig. 39 
and one in Fig. 42 (¢. m.). The multinucleate condition of 
so many of the formative cells must be regarded as preliminary 
to division, the division resulting in some cases in the pro- 
duction of the masses just spoken of. In other cases, where 
the formative cells, as such, have grouped themselves in the 
shape of a chamber, cell division merely leads to increase in 
the number of the enclosing cells. In other cases again, no 
doubt, the formative cells break up into finer cells, which 
separate and become scattered about. In whichever way they 
are used up, the number of formative cells, which is very large 
in the just attached sponge, grows steadily smaller during the 
production of the canals and chambers. The solid masses of 
small cells to which certain formative cells give rise, are irregu- 
lar in shape, and retain their connection with the cell network, 
Pl. XVII, Figs. 39, 40, and 41. The small cells of which such 
solid masses are composed quickly acquire the characteristic 
nucleus of the collared cell, and the mass itself constitutes the 
anlage of a flagellated chamber. I do not, however, believe 
that a single formative cell, unaided, gives rise to a flagellated 
chamber. On the contrary, I believe that several of the 
smaller solid masses of cells, each of which has been derived 
from a single formative cell, unites to form one of the larger 
masses, and this develops into a flagellated chamber. In look- 
ing over Figs. 39, 40, and 41 it is seen that the masses of cells 
are of various sizes ; and while it is permissible to assume that 
one of the smaller masses can reach by simple growth to the 
size of one of the larger masses, the close connection which 
exists between many of the smaller masses (c. #.’ in Fig. 39), 
coupled with the shape of some of the larger masses (an. f. c. 
in Fig. 39; this mass has already acquired its cavity), creates 
the impression that the latter have been formed by the fusion 
of the former. The solid mass of cells so formed acquires a 
central cavity, which at first is extremely small, ax. f. c., Figs. 
40 and 41. While the cavity is quite small, the surrounding 
cells are packed in several layers, but as the cavity increases 
