THE TANGANYIKA PROBLEM. 317 



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. 



