104 ART. 7. — I. IJIMA : HEXACTINELLTDA, IV. 



figs. 5, 6), giving support to the ectosome and the endosome 

 respectively, consist in the main of bundles of diactins, either 

 loose or compact, which are comparable to the smaller parenchy- 

 malia. Among themselves the hypodermal and hypogastral diact- 

 ins are of various sizes, with thickness reaching up to 30 //. 

 The shorter ones amongst them usually show a gentle annular 

 swelling around the spicular center. Hypogastrall}^ there not 

 infrequently occur diactins as short as, or at any rate not much 

 longer than, the axial length of the gastral hexactins, like which 

 spicules such short diactins may have microtubercles sprinkled 

 nearly all over the surface. Their appearance is such that they 

 might have arisen directly from the gastralia by loss of the four 

 rays in two axes. 



Hypodermal pentactins were discovered only in a limited num- 

 ber. There can scarcely be a doubt as to their being clearly dis- 

 tinguishable from the dermalia, though under certain circumstances 

 they seem to closely approach these both in size and appearance. 

 In them the unpaired proximal ray is the longest of all the five 

 rays ; it may be more than twice as long as the paratangential. 

 The latter, in one case measured, was 700 ii long and in another 

 case, considerably over that ; but it may sometimes be as short 

 as 300 IX. In short the size is subject to considerable variation. 

 The paratangentials are rough nearly throughout their entire 

 length, the roughness being quite similar to that of the dermalia, 

 while the proximal ray is generally smooth except towards the 

 end. 



The dermalia are predominantly pentactins (PL VIII., fig. 

 3) with a sixth ray represented by a small hillock-like promi- 

 nence on the distal side. In these the unpaired proximal ray is 



