16 AET, 5.' — SANJI HÖZAWA : 



are short but relatively wide. Diaphragm is present at each 

 apopyle. The nucleus of collar cells occupies an apical position. 



The gastral cortex is almost as thick as the dermal ; it is 

 perforated in a mesh-hke manner by irregularly quadrate, penta- 

 gonal or hexagonal openings (150-250// across) of exhalant canals. 

 The epithehum lining the gastral cavity and exhalant canals is 

 very conspicuous, the component cells being relatively large. The 

 apical rays of gastral quadriracliates, as they stand out into the 

 gastral cavity, seem to be covered all over by the epithelium. 



Skeleton (PL II., fig. 13). 



The dermal skeleton consits of triradiates, mieroxea and 

 the paired rays of subdermal pseudosagittal triradiates. The 

 triradiates lie parallel to the dermal surface with the basal rays 

 in most cases directed towards the sponge base. The mieroxea 

 are very small, numerous and thickly set. They lie in the dermal 

 cortex at varying angles to the external surface, beyond which the 

 outer ends freely project to a certain extent. 



In the middle parts of the sponge the tubar skeleton is 

 formed by the centripetal basal rays of subdermal pseudosagittal 

 triradiates, by the centrifugal basal rays of subgastral sagittal 

 triradiates, and by several intermediate rows of sagittal triradiates, 

 of which the basal rays are centrifugally directed. 



The gastral skeleton is chiefly made up of triradiates tan- 

 gontially placed without definite orientation and arranged in several 

 layers. It also contains the paired rays of subgastral triradiates 

 as well as large quadriradiates, the apical rays of which project 

 into the gastral cavity, pointing towards the osculum. 



The oscular margin is composed of trichoxea of varying thick- 

 ness running longitudinally and parallel with one another, and of 



