480 EIOHAED EVANS. 



These small spicules are not found in Spongilla moorei, 

 unless they are represented by those drawn in PI. 37, fig. 3, 

 J — /^ and fig. 4,7 — n, which is probably the case. However, 

 it must be admitted, 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 mega- 

 scleres 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 morpho- 

 logical character, and seems to break down in the Spongillidse, 

 whose Homorrhaphid ancestors were probably without micro- 

 scleres. 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 aspi- 

 nosa, 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, cylin- 

 drical branches which occasionally subdivide. These branches 

 grow from a thick basal membrane. Spongilla aspinosa, 

 however, at times forms merely a sheet which envelops 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 aspi- 

 nosa, 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 pale, according as they 

 grow in direct sunlight or in the shade. Owing to the depth 

 at which Spongilla moorei lives, the green colour of Spon - 

 gilla aspinosa would appear to be wanting. 



