73 



number of branch-rays than the main-rays of the other variety of codonhexasters. 

 I estimate the number of branch-rays on each main-ray at 30, so that the whole 

 spicule has 180 branch-rays. The rod-bells on the ends of the branch-rays are 

 only about 3 m long and half as broad. It is to be remarked that the terminal 

 bells of these small codonhexasters do not lie in one spherical surface but in six, 

 the centres of which are situated at the ends of the main-rays : the branch-rays 

 of each main-ray form part of a sphere. The external surface of the spicule is 

 consequently not a simple spherical one, but composed of six segments of spheres 

 the radii of which are represented by the branch-rays (pi. XII, f, 21). 



Other kinds of hexasters met with have simple, terminally-pointed branch- 

 rays of considerable length, which in their S-shaped curvature and calyx-like 

 arrangement resemble the branch-rays of floricoms. Of these hexasters two 

 different kinds, designated by me as drepanocoms and sigmatocoms, can be distin- 

 guished. Both are not nearly so frequent as the hexaster-form described above 

 and, particularly in the large specimen, are so scarce that one often seeks them 

 in vain in the microscopic preparations. Their non-occurrence in such prepara- 

 tions can therefore not be considered as a proof of their non existence in the sponge. 



The drepanocoms (from Sptn-an; scythe or sickle and xo/xrj hair) measure 60-70 f^ 

 in diameter. Their main-rays are slender, 8 /^ long and slightly thickened 

 at the ends. Each main-ray bears a terminal verticil of seven or eight branch- 

 rays. These are slightly curved, S-shaped and angularly bent below the distal 

 end, so that the terminal portion is directed backwards and the relative position 

 of the distal and central parts are similar to those of the shaft and blade of a 

 scythe. These branch-rays are very slender at the base, gradually thickened 

 towards the distal bend and up to this point 27 ^ long. The terminal blade-like 

 part is straight or only veiy slightly curved and gradually attenuated to a sharp 

 point (pi. XII, f. 16,17). One might consider these drepanocoms as belonging 

 to the same category of spicules as those floricoms, the branch-rays of which have 

 no terminal discs and bear at their ends, instead of a more or less circular, 

 marginally serrated plate, only a few, sometimes only two, elongated teeth, the 

 position of which is similar to the position of the distal recurved part of the drep- 

 anocom-branch-ray (pi. XII, f. 7). The drepanocoms of Didyaulus elegans 

 are similar to the hexasters of Eertwigia falcifera, described by 0. Schmidt as 

 " Sichelrosetten, " and found by me also in Trachyranlus gurlitti. 



The sigmatocoms are on the whole similar to the drepanocoms, differing from 

 them however by their considerably greater size and by the absence of an abrupt 

 bend in the branch-rays. Also in these spicules the distal parts of the branch-rays 

 are, although considerably longer, somewhat similar to scythe-blades, but these 

 are not attached to the proximal part of the branch-rays, as in a peaceful scythe, 

 but lie in the same direction and appear as a direct continuation of it, as in a 

 scythe converted into an implement of war. Thus the branch-rays are not 

 10 



