192 THE VOYAGE OF H.M.S. CHALLENGER. 



The parencliymal spicules supporting the soft body arc represented by a large number 

 of simple spindle-shaped diacts, varying in length up to 3 mm. Both their ends are 

 simply pointed or rounded off, and not unfrequently provided with small spines. While 

 most of these spicules appear to be smooth centrally, some exhibit there an annular 

 swelling, and others two opposite, or four cruciate tubercle-like elevations, into which two 

 or four cross branches of the axial canal are seen to penetrate. Even in the diacts 

 which are smooth centrally sometimes similar cross branches from the axial canal can be 

 detected.' 



The spindle-shaped spicules are, for the most part, not perfectly straight but slightly 

 bent, lying in strands or somewhat irregularly scattered. Slender diacts are also 

 occasionally to be found beset towards both ends wdth inwardly directed hooks 

 (PL XXVIl. fig. 3). Between the spindle-spicules there is a somewhat sparse 

 occurrence of proper oxyhexacts and derivative spicules, the latter with five to 

 three rays, or even with two opposed at right angles. Larger smooth hexacts very rarely 

 occur. Somewhat more abundantly, but yet rarely, slender hexacts are found with 

 distally directed teeth, as represented in PL XXVII. fig. 13. Similar hexacts with 

 curved rays (PI. XXVII. fig. 10), as figured by Max Schultze {loc. cit., Taf. iv. fig. 4), I 

 have only very rarely seen — so rarely, indeed, that I doubt whether they have not 

 found their way in from some other species of Hyalonema, and are not really foreign 

 to Hyalonema sieboldii. I am also doubtful whether the peculiar amphidiscs, 

 which were found so abundantly in the limiting membranes, are also proper to the 

 parenchyma. 



The dermal skeleton is mainly composed of strongly developed pentact hypogastralia, 

 which form by their mutually apposed tangential rays a comparatively wide-meshed 

 rectangular lattice-work, while the strands of the finer network of the skin are supported 

 by tangentially disposed diacts. The narrowed ends of the somewhat blunt rays are 

 frequently to some extent covered with tubercles, or are at least rough. They usually 

 exhibit the same character on the same pentact, but in diff'erent spicules vary so far at 

 least, that some are pointed and others quite blunt, some relatively smoother and 

 others more or less markedly beset with terminal protuberances. The distal (sixth) 

 ray has so completely disappeared that only the merest hint persists in the form of a 

 slight prominence. 



On the hypodermalia and on the dermal strands of diacts extended between 

 them there are seen countless autodermal pinuli, which are here exclusively 

 pentacts. The four basal rays intersecting at right angles lie wholly in the dermal 

 membrane ; the somewhat long distal ray, which is drawn out into a long fine point, is 

 always at right angles to the surface of the skin, and thus projects freely into the water 

 perpendicular to the body-surface. There is no proximal sixth ray, or its presence is 



' M. Schultze, Die Hyalonemeii, Taf. iii. and iv. 



