260 AKT. 7. — I. IJIMA : HEXACTINELLIDA, IV. 



As in R. victor the prostal pentactiiis seem to fall off readily. 

 Thus, in the specimen of PI. XX., fig. 1., in wliich the external 

 surface is in an almost perfect state of preservation, the pent- 

 actins, protruded to an extent of 3 or 4 mm., occur isolatedly and 

 sparsely in certain parts only, while over the greater part of the 

 sponge they are totally missing. 



The delicate dermal lacework is thrown into little creases, 

 possibly as the result of desiccation. Observed under the lens 

 the meshes appear to be irregtdar and indefinite in shape, which 

 is due to the fact that the dermalia are diactins that cross, 

 or are joined to, one another at various angles (PL XX., fig. 12). 

 The thin and wavy hypodermal strands, in places so thin as 

 even to closely resemble tlie dermalia in strength, form also 

 irregularly angulate, but of course much larger, meshes. They 

 are seen, sometimes with a fair degree of distinctness, to converge 

 towards separate central points which are 3-6 mm. apart. This 

 is on account of the pentactinic hypodermalia being arranged in 

 groups, much as we have seen them in R. victor. In the lower 

 parts of the sponge, especially near the base, the centers of the 

 hypodermalia groups are usually well indicated by short small 

 projecting tufts of fine needles which either cohere or are loose 

 and brush-like. The same tufts we have likewise seen in R. 

 victor. The prostal pentactins that may occur spring out in 

 connexion with the tufts. 



In one specimen I have seen on the dermal surface several 

 cicatrice-like spots which appeared white and densely textured. 

 The same have sometimes been noticed in several other Acan- 

 thascinse. It is more than probable that they arise by hyper- 

 regeneration of tissues, both soft and scierie, at places where the 

 sponge had suffered an injury. 



