130 AET. 7. — T. IJIMA : ITEXACTINELLTDA, IV. 



spindle-like, bow-like or boomerang-like ; in the last case they have 

 an elbow-like bend in the middle. They gradually taper towards 

 both pointed ends ; the surface is in most cases smooth through- 

 out ; the spicular center is never marked by a swelling in the 

 external contour. 



The comitalia, i.e., the finest parenchymal diactins directly 

 surrounding the principalia, are filamentous spicules which are 

 nearly uniformly thin throughout and are subterminally always 

 rough-surfaced, ending with rounded or conically pointed tips. 

 They may sometimes show either an annular swelling or four 

 boss-like prominences around the spicular center. The principalia 

 and the comitalia arc in all cases intergradationally connected by 

 such diactins as are intermediate in form and dimensions. 



Certain parenchymalia under special circumstances seem to 

 become protruded on the external side of the body-wall and thus 

 form the diactinic needle-like ])ro8ial\a found in a number of 

 species. In certain Staurocrihjptm and Rhabâocalyjitus the pros- 

 talia of the kind in question are present on all parts of the 

 body as long as the sponge is young and small (PL XV., fig. 3 ; 

 PI. XXIL, figs. 3-5 ; etc.) ; but with growth of body, they are 

 either lost or l)ecome restricted to the oscular margin where they 

 may form an ill-defined jialissade-like fringe {marginalia). 



A hypodermal system of spicules is always differentiated. 

 For Acanthascus it is characteristic that the hypodermalia consist 

 exclusively of diactins. In both Sfauyocah/ptus and BJiabdocalyptus 

 they consist of moderately large pentactins, of which the cruciate 

 paratangentials, representing two complete axes, support the dermal 

 layer either alone by themselves or in union with a greater or 

 less quantity of diactinic hypodermalia. The paratangential rays 

 of individual pentactins, which are smooth or shagreened or else are 



