CALYCOSILVA CANTHARELLUS. 89 



to the clavules with twisted branch-rays of Farrea occa claviformis and the 

 helonychhexasters above described. The discohexasters with spirally twisted 

 end-ray verticils of Herlwigia falcifera, Rhabdopedella tintinnus, and Saccocalyx 

 pedunculata and the clavules with similarly twisted branch-rays of Farrea con- 

 volvulus on the other hand do not appear to be associated with regular, not 

 twisted spicules of the same kind. 



In studying the question how these spirally twisted spicules have been 

 produced I gained the impression that the parts of the living mass ^ which built 

 them must have changed their relative positions in a torsional manner during 

 the growth of those rays or portions of rays which are spirally twisted in the 

 full-grown spicule. In the case of the oxyhexasters, helonychhexasters, and 

 clavules with spirally twisted branch-rays there is only one torsion-axis corre- 

 sponding to one of the axes of the spicule, and in these the torsion seems to 

 have affected the whole living mass uniformly. In the case of the discohexasters 

 there are six torsion-axes of this kind, corresponding to the axes of the six main- 

 rays,, and six different torsional systems in the living mass. 



In speaking of the spirally twisted oxyhexasters of Rhabdocalyptus mollis 

 which were found in some, but not in all specimens, Ijima ^ says : "I am therefore 

 disposed to consider them as of inconstant occurrence in the species. Possibly 

 they are produced only under certain abnormal conditions." Also in Calyco- 

 silva cantharellus they have been found in one specimen only. Since, however, 

 this was obtained together with the others destitute of these spicules in the 

 same locahty, at a considerable depth, where doubtless the environment was 

 very monotonous, it is hardly to be supposed that the external influences acting 

 on it could have been in any way different from the influences acting on the 

 others. A spiral twisting of some of the spicules is, as the above statement 

 shows, if not a frequent, still a widespread occurrence in hexactinelUds. It 

 seems therefore improbable that the spiral twist is produced through the influence 

 of abnormal conditions, and to be considered as an abnormity. Neither can it 

 be ascribed to obstacles preventing the (twisted) rays from growing in the 

 usual direction, because, in the first place, there are no such obstacles, and 

 because, in the second place, their presence could not affect all the actually 

 twisted rays of a spicule in the same way and induce them to curve round spirally 

 in the same direction. 



' I use the expression " living mass," because I do not know whether these spicules are built by 

 distinct cells, and if so, by how many, or by syncitia, and if so, how many nuclei or chromidia or other 

 centres of vital action, these syncitia contain. 



2 /. Ijima. Studies on the Hexactinellida. IV. Journ. CoU. sci. Tokyo, 1904, 18, p. 266, 267. 



