126 ART. 7. — I. IJIMA : HEXACTINELLIDA, IV. 



The microdiscohexaster (PI. X., fig. 8) is relatively very small, 

 measuring only 20-23 n in diameter. It is an exceedingly deli- 

 cate object and might easily escape attention. Spherical in shape, 

 it is of the usual appearance and structure, so that a special de- 

 scription appears superfluous. I have found them on tlie whole 

 sparsely distributed in the gastral memljrane, though in some 

 parts of it they are rather common. They occur also in the 

 dermal membrane but exceedingly rarely. 



Soft Parts. 



The collector of the Sei. Coll. specimen had ])ut a small 

 piece cut from it into alcohol at the spot of capture ; so that, I 

 was enabled to make some observation on the soft tissues stained 

 and sectioned in the ordinary way. 



The dermal membrane is film-like, perforated by large and 

 mesli-like pores. 



The trabeculse are thin, though in places membranously ex- 

 panded. They form a dense cobweb at the jiillars joining the 

 ectosome to the choanosome (PI. X., fig. 12) and also in the 

 subgastral space. 'J he cobweb is borne on the free proximal rays 

 of the gastralia in a tent- like manner (PI. X., fig. 13). The 

 well-stained trabecular nuclei measure about 2? //. 



Archseocytes are met with in small groups on the outside of 

 flagellated chambers (PI. X., fig. 15). Thesocytes with well- 

 stained spherical contents, are present in some numbers. 



The chambers show the usual shape and arrangement (PI. 

 X., fig. 12). They are cup-like or glove-finger-like with a dia- 

 meter of about 140 p.. Their wall (PI. X., fig. 15) is 0])en- 

 meshed, the beams being thin, finely granular and but little 



