igiS-] N. ANNANDAI.E: Notes on Freshwater sponges. 



239 



with the basal membrane, which also contains spicules in consider- 

 able numbers. 



Spicules. — The macroscleres are small and moderately slender, 

 varying greatly in size but not exceeding o'i47 mm. X 00 168 

 mm. Their ends are blunt and often more or less inflated. Their 

 surface is covered uniformly with minute rounded prominences, 

 but they do not bear sharp outstanding spines. As a rule the 

 main axis is curved, but never very strongly. 



The gemmule-spicules are very like those of the skeleton but 

 smaller, and as a rule relatively less slender. They are never more 

 than 0-0842 mm. long by 0-0126 mm. broad but vary greatly in 

 size and proportions. Deformed spicules and irregular spheres are 

 not uncommon among them. 



The only free spicules are the minute amphidiscs characteristic 



Spicules of Corvospongilla scabrispiculis, x 240. 



of the genus Their shafts are very slender, either straight or 

 curved and as a rule about 0-025 mm. long. The termuial spmes 

 are fairly short and less retroverted than m some species. 



Gemmules.—'The gemmules, which are very numerous, form, 

 together with the cages in which they are held, a regular pavement- 

 layer and adhere firmly. Each is enclosed in a separate loculus 

 which has a roof of spicules and membrane and a floor formed of 

 the basal membrane of the sponge. The walls and roof are com- 

 posed of two lavers of macroscleres lying parallel to the surface of 

 the sponge and crossing one another without protrudmg from the 

 membrane. There is a circular aperture in the roof through which 

 the foraminal tubule of the gemmule protrudes. Each gemmule 

 has a thick chitinous outer coat in which its proper spicules are em- 

 bedded horizontally and somewhat sparsely ; it bears a single 



