0(3 THE VOYAGE OF H.M.S. CHALLENGER. 



ill the various species examined (over 60) is so varied as to supply valuable characters 

 for the identification of species. It must, however, be stated generally that the 

 spines vary very considerably in length and shape in almost every species examined. 

 Whatever may be the form of spine possessed by any particular species, whether 

 triangular, cylindrical, or knobbed, the specific features are never well marked at the 

 apex of a branch. If one follows the contour of the spines from the apex of a branch 

 downwards to its base, and on to the main stem if need be, a variety of outline is 

 presented which may be conveniently divided into two sections, progressive and retro- 

 gressive. In the Schizopathinse, in which the apical portion of a branch is usually 

 membranous for a considerable distance, the first formation of spines is more easily 

 traced. They arise first as longitudinal thickenings of the sclerenchyma, which are 

 usually very narrow. The deposition of additional layers causes an increasing thicken- 

 ing of the central portion of each ridge, so that gradually a spine is evolved which varies 

 in size, shape, &c, according to the species. The longitudinal ridges may remain, 

 connecting a series of spines in irregular longitudinal series, or may become lost 

 altogether. In any case the spines become elaborated up to a certain point, which may 

 be considered " normal." The distance from the apex at which the first normal spines 

 occur is very variable, and is certainly much greater in most Schizopathinge than in 

 the Antipathinas. From this point onwards for a variable distance the normal character 

 is maintained, although irregularities of arrangement may occur. In still older portions 

 of the corallum the normal character is lost and the retrogressive period sets in. Perhaps 

 the most typical form of retrogression is to be found in such forms as Parantipatlu-s 

 larix, in which the normal spines are elongate, somewhat cylindrical, and tapering. In 

 this case each new layer of sclerenchyma adds a new film to each spine, which in conse- 

 quence becomes gradually reduced in length, and assumes a more stunted form with a 

 broader apex. A continuation of this process may reduce the spines on the stem to the 

 form of granules, or they may be obliterated completely as in Leiopathes glaberrima. 

 This, however, is not the only means by which the " normal " character is lost. In 

 some cases it appears as if the secretive power of the axis epithelium of a spine more than 

 keeps pace with that of the general surface of a branch, and that additions may be made 

 to the apex of a spine without materially increasing its thickness below. For example, 

 in Antipatliella subpinnata the spines on the main branches are longer and relatively 

 more slender than those above. In other cases the spines near the base of a 

 colony become much elongated and dendritic ; such is the case in Antipathes spinosa 

 and Antipathes myriophylla. Forked spines are of frequent occurrence in many species 

 as an abnormality (?), but in Stichojxithcs gracilis this feature is normal, and leads to the 

 formation of double spines. At first all the spines are simple and subtriangular, a little 

 lower down certain spines become bifid at the tip. The layers of sclerenchyma subse- 

 quently formed make this bifid character more pronounced, and also tend to cover up the 



