6 Airr. 7. — I. ijiMA : hexactinellida iv. 



persist even wlieii the sponge lias attained the size of a pea or 

 of a bean. This is attested by two specimens of the size in- 

 dicated, which I have found in my collection. In both the 

 sponge- wall is simply thinned out, without being broken through, 

 at the point where one would expect tlie formation of the oscular 

 aperture. Though I have not examined them on sections, I 

 believe that the wall there lacks the chamber-layer as represented 

 i)y F. E. HcHULZE in his fig. 5, PI. LIII. {I. c), and further 

 that, in the absence of a single large aperture, the discharge of 

 water from the gastral cavity must have taken place through the 

 intertrabecular gaps of that part of the wall. All the I'est of 

 my specimens, including the smallest of G or 7 mm. height, show 

 an open osculum. 



In some specimens I have seen the external surface covered 

 partly or nearly all over with a veil, formed of small hypodermal 

 pentactins which had protruded through the dermal layer. Ho, 

 for instance, in two of the specimens figured on PI. I. All the 

 smaller specimens are without the veil. Not that all the larger 

 specimens are provided with it ; on the contrary, the two largest 

 specimens, respectively 19 mm. and 22 nun. high, seem to show^ 

 J 10 trace of it. Presumably it is formed only under certain 

 circumstances after the sponge has reached maturity. In forming 

 it, the hypodermal pentactins stand out isolatedly but usually at 

 such intervals that their para tangential s are nearly or quite in 

 touch with one another. Their shafts are exposed over the dermal 

 surface to a length of 2 — 1 mm. 



The real derjnal surface is smooth. A\^hen dried it is some- 

 what shin}', which is however by no means a peculiarity of the 

 genus or of the species. The reflection of light takes place 

 principally, if not solely, from the smooth Ijardened surface of 



