566 studies on sponges, 



Skeleton. 



The skeletou consists of the hulh ac. and tr. ac. spicules ah-eady 

 desciibed by Bowerbank and O. Schmidt of their genera Raphyrus 

 and Papillina, to which two other kinds of spicules, observed in 

 our species, must be added. 



Surface Skeleton. 



The surface of the hard projecting ridges in the surface net is 

 occupied by a number of small spicules, which form a layer about 

 0-06 mm. thick. (Fig. 16.) These spicules (figs. 13, 14) are very 

 variable in their shape, straight or curved, with large and irregular 

 spines all over the surface and particularly at the ends. They 

 could be termed tr. tr. sp. They are of very uniform size and 

 measure 0'03 mm. in length and 0*007 mm. in thickness. Besides 

 forming a dense armour on the projecting ridges they are found 

 scattered also in the concave membranes of the meshes. 



Skeleton of the Hard Fibres. 



The main support of the whole sponge is constituted by a 

 reticulate mass of truncate and bulbous spicules, which are mostly 

 situated longitudinally, and disposed in such a manner as to jjoint 

 towards the free surface (fig. 16) in the projecting ridges, or towards 

 the pulpa in the meshes in the interior. 



These spicules are not cemented together by any horny substance. 

 They are very abundant, and form hard, dense masses (fig. 16) 

 throughout the fibres of the interior. Scattered, these spicules are 

 also found rarely in the soft pulpa of the meshes in the interior. 

 These spicules are of uniform size 0-5 mm. long and 02 mm. 

 thick. They are cylindrical and al>ruptly pointed (fig. 9.) The 

 bulb of the majority of spicules measures 0'03 mm. in diameter. 

 Sometimes it increases to a diameter of 0"0036 mm., and may have 

 indications of points at its greatest diameter (fig. 10.) 



One of these points may grow out to form a spine 0'09 mm. long 

 (fig. 11.) This however, is rare. 



On the other hand the bulb may be absent altogether. Tr. ac. 

 spicules are not unfrequent. 



