THE TANGANYIKA PROBLEM. 
3i7 
as has been done by Potts, that in both cases these small 
spicules may be young megascleres, and not microscleres. 
The only distinction obtaining between megascleres and 
microscleres, viz., that the former are bound up in the 
general skeleton of the sponge while the latter lie scattered 
about freely, is a functional rather than a morphological 
character, and seems to break down in the Spongillidse, 
whose Homorrhaphid ancestors were probably without 
microscleres. The consequence of this is the impossibility 
of deciding definitely the true character of certain spicules. 
It seems, however, a safe conclusion that these small spicules 
are the same in Spongilla moorei as in Spongilla aspinosa, 
though in the former they are not found in the dermal 
membrane, their place being taken by the cuticular layer of 
spongin which covers the surface. 
The form of growth of these two species appears to differ. 
Spongilla aspinosa is provided with long, slender, cylindrical 
branches which occasionally subdivide. These branches 
grow from a thick basal membrane. Spongilla aspinosa , 
however, at times forms merely a sheet which envelopes the 
support on which it grows, while Spongilla moorei in all 
the specimens examined presented this appearance. 
The spongin has not been described in Spongilla 
aspinosa , and therefore neither comparison nor contrast 
is possible. 
The colour of Spongilla aspinosa is said to be green, a 
fact which is the result of the position in which it grows, for 
Spongilla lacustris and Ephydatia miilleri and fluviatilis 
may be either green or brown, according as they grow in 
direct sunlight or in the shade. Owing to the depth at 
which Spongilla moorei lives, the green colour of Spongilla 
aspinosa is wanting. 
