TWO NEW SPONGILLZE FROM LAKE TANGANYIKA. 477 



thickeued at the points where the conuecting spicules occur^ 

 these being either partially or completely surrounded by it 

 (PI. 38, figs. 6 and 7). Not only are the fibres and the con- 

 necting spicules enclosed in a sheath of spongin^ but the 

 surface of the sponge is covered by a thin layer or cuticle of 

 the same substance, which dips down between the cells of the 

 dermal membrane, and communicates with that which envelops 

 the fibres (PI. 38, fig. 6). 



(3) The Canal System. — Owing to the fact that the 

 material which had been preserved for histological study of the 

 sponge had been shaken considerably in moving from place to 

 place, a great number of cells had apparently become loose, 

 and were found lying in the spaces of the canal system. In 

 consequence it was impossible to make a complete and thorough 

 study of that system, though individual cells were in many 

 places nicely preserved ; nor is Spongilla, for other reasons, a 

 favourable object for the study of the canals in the Monaxonida. 



The canal system in Spongilla moorei belongs to the 

 type usually described as the third. The dermal pores, which 

 are situated on the flanks of the mound-like elevations of the 

 surface and in the intermediate depressions, are small, and open 

 into the subdermal cavity, which is lined by flattened epithelium, 

 and considerably reduced by the passing through of the skeletal 

 fibres, which are enclosed in a sheath of spongin, which is 

 covered by cells of the epithelial layer. 



The inhalant canals which pass from the subdermal cavity 

 into the chambers are narrow and difficult to make out. In 

 some cases these canals are short, owing to the flagellated 

 chambers being situated close to the floor of the subdermal 

 cavity. Those canals which pass into the chambers which are 

 situated more deeply in the sponge are long and narrow, follow- 

 ing a winding course, and keeping nearly always between the 

 chambers and the fibres of the skeleton. On their way down 

 into the deeper parts of the sponge they give off branches which 

 open into the chambers by way of prosopyles, which are so small 

 that it is almost impossible to make them out. The apopyle 

 was easily distinguishable as a wide opening, comumnicatiug 



