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



polyp walls, wliicli are penetrated by endodermic canals, buds arise. These sometimes 

 develop into simple polyps, but sometimes form long polyp-tubes, which again give off 

 lateral buds. The walls of the polyp calyces, into which the anterior tentacle-bearing 

 oral portion may be completely retracted, contain spicules. In some species these form 

 a continuous network, in others, they are more loosely disposed, and in part are united 

 together by a horny substance. In both cases, the mesodermal layer of the calyx wall 

 acquires a tubular and rigid character. In all cases there can be distinguished (1) principal 

 polyps which form the stem and branches of the colony; these may be termed axial 2>oly})s 

 of the first and second rank, and (2) lateral i^olyi^s which are disposed upon the former, 

 usually in spirals. The axial polyps form long tubes with stiffened walls, which are 

 thickened from the apex towards the base. The upper hollow portion, which includes the 

 oral cavity along with the crown of tentacles and the oesophageal tube, is soft, and either 

 beset with loosely disposed spicules, or is altogether without them ; it can be retracted 

 into the calyx tube in the same way as in Clavularia. The alimentary cavity of the 

 polyp extends the entire length of the calyx tube ; the mesenteric folds are limited to 

 narrow ridges. According to Koch, in Telesto j)'>'olifera only two dorsal folds are 

 continued down to the bases, while the other six cease much sooner. In another species, 

 Telesto arhorea, n. sp., the mesenteric folds form narrow creases which may be followed 

 to the base. Sj)icules occur throughout the entire calyx wall, and in Cary'oa are united 

 together by a horny substance. 



The calyx wall furthermore contains a canal-system, consisting of fine endodermic 

 canals, which are in communication with the alimentary cavities of the axial polyps. 

 From these there arise the buds of new polyps, which sometimes remain short, and 

 sometimes develop into long axial polyps of the second order. The latter again produce 

 buds, from which axial polyps of the third order may arise. In some species the axial 

 polyps appear to produce no generative elements, which then seem to be restricted to 

 the secondary individuals. This is the case in Telesto arhorea, n. sp., where an alterna- 

 tion of generations might therefore be said to occur. 



Subgenus Telesto, s. sir. ( = Telesco, Gray). 



The axial polyps spring from stolons or basal prolongations which spread over foreign 

 bodies ; they are not very long, and they give origin, on their side walls, to polyps going 

 off at right angles, and differing but little in form or in size from the axial polyps. These 

 polyps may, in their turn, bear accessory pol^'ps. The whole colony is low and only slightly 

 ramified. The calyx wall is for the most part marked by eight longitudinal ribs, with 

 corresponding furrows. The spicules form broad, dentate discs, or ramified, irregular 

 bodies, whose spines interlock so that a continuous layer is formed in the mesoderm. 



