No. 3. ] DEVELOPMENT OF MARINE SPONGES. en 
are not nuclei, but are products of cell metabolism. He 
further believes that these cells (formative cells) do not give 
rise to the flagellated chambers. For a statement of his views 
on this head, see p. 319. 
Now, the precise way in which the flagellated chambers are 
formed in Esperella depends on the behavior of the formative 
cells. The simplest way in which a chamber is ever formed 
is for several formative cells to group themselves together in a 
hollow sphere, f. ¢c.’and'f. c."" in Pl. XVII, Fig. 42, and /. c. in 
Pl. XVII, Fig. 39. They then divide up into smaller cells, which 
gradually acquire the characteristic features of collared cells. 
In the chamber /. c.", Fig. 42, the division into smaller cells 
has already progressed to some extent, but the cells still retain 
their rounded independent shape, one of them remaining much 
larger than the others. In the surface view, Pl. XVIII, Fig. 57, 
a number of chambers are shown which, I take it, are being 
formed in the manner described. In fic’, fi.c.", f. c.!" the 
formative cells are as yet only loosely combined, especially 
loosely in f.c.’ In fc.’ the connection between the separate 
cells is a closer one, and some of the cells have divided, as is 
evidenced by the difference in size. In most of the other 
chambers, of which f. c... may be taken as an example, the 
division of the cells has been carried so far that they are 
tightly compressed and more or less columnar. Early in the 
development of the chamber the nuclei acquire the character- 
istic appearance of the nuclei of collared cells, becoming small, 
and staining very deeply. The development of the collar I 
was not able to follow. As formed in this way, a flagellated 
chamber is nothing more than an intercellular space or lacuna, 
and in its first stages is essentially similar to a canal (compare 
in Fig. 42 the canal caw.’ and the chambers /. c.’ and f. c."), 
the lacuna becoming the cavity of the canal or chamber 
respectively. This means of producing flagellated chambers 
is only employed in the early stages, directly after fixation. 
In a few sponges, at this time, it seems almost the only 
means employed, but in most individuals it is made use of 
side by side with another method, which I shall now 
describe. 
