288 WILSON. PVOL. EXs 
through a region in which few or no gemmules appear (Pl. 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 Pl. XIV, Fig. 8, and 
Pl. 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 g’, Pl. XIV, Fig. 8, and g’, Pl. 
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, 
