288 WILSON. [Vol. IX. 



through a region in which few or no gemmules appear (PI. XIV, 

 Fig. 2). In the latter the trabeculae are made up chiefly of 

 rows of flagellated chambers, with but a scanty amount of 

 mesoderm between the chambers. But in the former the 

 flagellated chambers are either absent or are very few in 

 number. The trabeculae in such a region are composed of 

 mesoderm, with gemmules, and a flagellated chamber here and 

 there. What I take to be the remains of degenerated flagel- 

 lated chambers are scattered about through the mesoderm. 

 Such are the groups of cells, deg.f. c, in PI. XIV, Fig. 8, and 

 PI. XV, Fig. 15. The cells composing such groups are quite 

 like the lining cells of the chambers in general appearance, that 

 is, they have a small clear body which stains scarcely at all and 

 the peculiar nucleus of the collared cell. The inference from 

 these data is that where gemmules begin to develop in large 

 numbers, the flagellated chambers of the region degenerate. 

 What becomes of the collared cells I cannot say, but Metschni- 

 koff's observations on the disappearance and reappearance of 

 the flagellated chambers in young spongillas (12) make it 

 probable that these cells are transformed into amoeboid meso- 

 derm cells. Where gemmules are very numerous, the trabe- 

 culae themselves are ruptured and broken down in many 

 places. This is the natural result of the compression of the 

 tissues due to the growth of the gemmules, in the course of 

 which many of the neighboring smaller canals are obliterated, 

 and of the liberation of the gemmules. In such spots the 

 sponge body consists of scarcely more than an amorphous 

 aggregate of cells and gemmules, and affords a noticeable 

 appearance of degeneration when compared with the smoothly 

 outlined trabeculae of a non-gemmular district. 



Very young gemmules, such as_o-', PL XIV, Fig. 8, and^', PI. 

 XV, Fig. 9, are composed of a small number of polygonal cells 

 surrounded by a follicle of flattened cells {g.f.). I have never 

 found a gemmule surrounded by a follicle to have less than five 

 cells in cross section. The bodies of the gemmule cells are 

 filled with a finely granular yolk, and take the stain well (hae- 

 matoxylin or carmine). The nuclei are always conspicuous but 

 differ much in appearance, the difference being due, as I think, 



