76 RICHARD EVANS. 



swollen at both ends to the fully-formed amphidiscs. Their 

 development, however, will be considered along with that of 

 the gemmule. 



B. The Arrangement of the Spicules to form 

 Fibres, etc. (PI. 1, fig. 2). — The spicule fibres are poorly 

 developed, and consequently stand in a most marked contrast 

 with those of some other fresh-water sponges. I have never 

 seen more than three spicules situated side by side in a 

 spicule fibre, and scarcely ever saw more than two. As often 

 as not, the spicules seem to be arranged end on in a single 

 file. In the deeper parts of the sponge, fibres are almost 

 non-existent, the spicules lying about freely and presenting 

 no particular arrangement. Nearer the surface, however, the 

 fibres are better developed, and traverse the strands of tissue 

 which separate the various compartments of the sub-dermal 

 cavity from one another. On the outer ends of the fibres is 

 situated the dermal membrane, which is often pierced owing 

 merely to the wear and tear of the life which the sponge 

 lives. Owing to the absence of flesh spicules or microscleres, 

 the skeletal fibres formed of megascleres present an evident 

 tendency to run in the vicinity of the membranes which line 

 the canals and cavities of the sponge. 



As has been stated above, spicules of the class h take no 

 part in the formation of the skeleton, but this is not true of 

 those belonging to class c, i. e. the amphidiscs. The latter 

 are found in all stages of development scattered about in the 

 general tissues of the sponge, while the former are limited to 

 the walls of the enigmatic bodies described above. Special 

 stress must be put on the fact that the developing stages of 

 the amphidiscs have been seen in the sponge tissues, and 

 not in the gemmule wall. 



c. Spongin. — It is scarcely necessary to mention spongin 

 in connection with Ephydatia blembingia, for it is almost 

 completely absent. In this respect the sponge here described 

 strongly contrasts with some fresh-water sponges. In 

 Spongilla nioorei the spicule fibres and the dermal mem- 

 brane are covered with this substance (7), but in Ephy- 



