312 WILSON. [Vol. IX. 



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 {c. 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, 

 PI. 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. m.' 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, an. 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 



