102 ART. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



preserved, I should think it would be rather inconspicuous be- 

 cause it closely overlies the choauosoinal surface in parts and the 

 cobweb-like hypodermal framework in other parts. 



Some deep and chasm-like slits occur on the external surface, 

 their wall presenting a granular appearance. This is due to 

 broken ends of the parenchymalia which there appear to be even- 

 ly nipped off. The slits were evidently made by Ophiurons 

 which took their abode in the sponge, as is apparent from such 

 as still contain that animal. 



The gastral surface (PI. YIII., fig. 4) is in a much better 

 state of preservation. The excurrent canalar apertures, of very 

 various sizes under 18 mm. diameter, are covered over witli an 

 endosomal latticew^ork composed mainly of moderately strong and 

 compact strands which may be called hypogastralia. The meshes 

 are angular but irregular in shape, mostly measuring 1-3 mm. 

 in length of sides. They are all open, which I believe is the 

 natural state. At any rate, the gastralia proper are only found 

 either distributed singly on the beams, or several together on the 

 nodes, of the hypogastral latticework. 



Remarkable is the fact that under certain circumstances the 

 above endosomal latticework, instead of extending merely in a 

 plane layer, may be developed more or less in the third dimen- 

 sion also so as to form a trabecular system of some thickness. 

 Thus, I have seen some cases of the excurrent canalar apertures 

 being incompletely closed, so to say, by a spongy partition. 



The larger the excurrent aperture, the deeper is the pit-like 

 canal it leads into. Usually about half-way through the sponge- 

 wall, the larger canals begin to divide uj) into branches. And 

 these branches, unless they happen to be small, are seen to begin 

 with apertures which are spanned by essentially the same lattice- 



