214 ART. 7. — I. ijima: HEXACTINELLIDA, IV. 



90 [i, but are usually thinner. The major part of the length is 

 protruded free, while the part rooted in the wall is accompanied 

 by fine comitalia. 



The hypodermal'ia, which go to form the hypodermal strand.*, 

 are pentactins and diactins, in both of which the rays are al- 

 ways smooth except at the roughened ends. The extreme tip of 

 the rays is either rounded or conically pointed. 



The hypodermal pentactins are of a large size. The curved 

 or nearly straight paratangentials may be 8 mm. long with a 

 breadth of 80 // at base. The unpaired proximal ray, which is 

 always straight, is much longer and is invested with fine comital 

 diactins in the usual manner. This ray, together with the roots 

 of the diactinic prostalia that may ])e present, forms a part of 

 the so-called pillars. Seen on the sponge surface, the centers of 

 hypodermal pentactins are situated either isolatedly or a few 

 together in loose groups. Their loose arrangement sufficiently 

 accounts for the fact that the four paratangentials in a spicule 

 generally have a regularly cruciate disposition, each being free 

 to take its natural direction during development (cfr. p. 131). Only 

 occasionally have I met with such hypodermal pentactins as have 

 paratropal paratangentials. 



In certain very small specimens I ascertained that the hypo- 

 dermalia consisted of pentactins alone. Some of these showed 

 paratangentials with microtubercles sparsely distributed throughout 

 the length, and seemed to intergrade with the larger dermalia. 



Whereas, in all the larger specimens the paratangentials 

 of hypodermal pentactins are usually accompanied by a greater 

 or less number of slender diactins, which are scarcely distinguish- 

 able from parenchymalia of similar dimensions. In some places 



