No. 3-] DEVELOPMEXT OF MARINE SPONGES. 311 



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, /. c' and /. f." in PI. XVH, Fig. 42, and /. c. in 

 PI. 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 /. c.\ f. c", f. c!" the 

 formative cells are as yet only loosely combined, especially 

 loosely in /. c' In /. c." 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 /. <:."' 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 can.' and the chambers /. c' and /. 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. 



