60 AÈT. 1. — I. IJIMA : HEXACÏINELLIDA, III. 



slight siibterminal swelling. The surface for a sliort distance 

 from the end is always roughened by the presence of niicrotu- 

 bercles. 



A parenchymal hexactin may attain a considerable size. 

 One of the largest I have picked out from a large specimen had 

 rays as long as 7 mm. and 70 !'■ thick near the central node. 

 But the majority are much smaller and more slender-rayed, leading 

 down to such oxyhexactins as will later be described as the 

 canalaria (PI. IV., fig. 8; PI. V., fig. 12). The hexactins, when of 

 a small size, present a regular or nearly regular appearance, but 

 are otherwise more or less irregular, not only in that the rays 

 are bent — sometimes strongly bent — but often also in having rays 

 of unequal lengths (PI. IV., fig. 6). This inequality may be 

 sufficient to give a stump-like appearance to some lays in com- 

 parison wdth the others in the same spicule. It even leads over 

 to cases in which one or more rays are reduced to total atrophy ; 

 so that, besides the hexactins and diactins there are to be met 

 with among the parenchymalia such intermediate forms as are to 

 be called pentactins, tetractins and triactins (PI. IV., fig. 5, h-d ; 

 PI. v., fig. 12). The tetractins are represented either by' staur- 

 actins or by those formed by suppression of two rays belonging 

 to difterent axes. The triactins are usually tauactins, seldom the 

 other form composed of rays representing three half-axes. — The 

 abortive development as well as the crooked state of the rays in 

 many of the above parenchymalia evidently stands in relation to 

 the thinness of the choanosomal septa, which ill affords sufficient 

 space for their free and natural development. Nevertheless, 

 parenchymalia are occasionally found which project one or more 

 of the rays l)eyond the septal surface and freely into canalar 

 lumen. For instance, in fig. 12, PI. V., which represents the 



