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



1*1. LVIII. iii;s. 1, 3 — cd; PI. LXII.) ; and he therefore considered them as belonging to 

 the perisomatic system, on the ground of their not being thickened by the peculiar fascicu- 

 lated tissue of parallel rods such as is found in the growing stem- and arm-joints. He 

 described this fasciculated tissue as appearing in the first radials. But according to 

 Dr. Carpenter " there is no distinction in texture between, the endogenous additions by 

 which the first radials and the basals are respectively thickened ; so that we cannot place 

 them in separate categories on this score. But further, we have seen that in the stage 

 now described, the basals as well as the radials are perforated to give passage to the 

 radiating extensions of the sarcodic axis of the stem, which only reach the radials through 

 the basals ; so that this ground of distinction also fails to separate them." 



The basals and radials form part of the apical or abactinal system of the Crinoid, and 

 are represented by the genital and ocular plates of the Urchins, and their homologues in 

 the other Echinoderms.^ The oral plates of the Crinoid correspond in like manner with 

 the mouth-shields of Ophiurids, the " odontophores " of Asterids, the oral plates of the 

 Psolidse, and possibly also with the five actinal plates of Palceostoma mirabilis among the 

 Urchins.^ As regards the rest of the Crinoid skeleton, however, nothing more than a 

 very general homology can be established with the skeleton of the other Echinoderms. 



The perisomatic skeleton consists essentially of numerous minute plates which are 

 usually more or less isolated, but sometimes slightly connected by fibrils of connective 

 tissue (PL VI. fig. 4 ; PI. XVII. figs. 6-10 ; PL XXVI. figs. 1, 2 ; PL XXXIII. figs. 6, 7 ; 

 PL XLL figs. 4,^2-14; PL XLIII. fig. 3; PL XLVIL figs. 10-13; PL L. figs. 1, 2; 

 Pis. LI v., LV. ; PL LVII. fig. 3, an; PL LXIL). The radial skeleton, however, consists 

 of successive joints and rods which are developed in a longitudinal direction, and are 

 united to one another by articulation or suture. In either case the ultimate imion of the 

 two joints is efl!ected by means of connective tissue fibres, which pass from the nucleated 

 and pigmented organic basis of the one joint into that of the other (PL Vllb. 

 figs. 1, 8, li, Id. PL XXIV. figs. 6, 7 ; PL LVIII. figs. 1-3—^, Ih, L). These fibres are 

 sometimes quite short, and their ends are surrounded by the denser layers of calcareous 

 reticulation on the apposed surfaces of the two joints, which are thus closely and 

 immovably fitted together, though they can be separated by the action of alkalies. 

 This mode of union is called a " suture," or better, a " synostosis." ^ 



The first i-adials of the Comatulse are connected in this manner both with one another 

 and with the centro-dorsal. The same mode of union also occurs between the radials of 

 the Pentacrinidse and the basals on which they rest, as well as between the five individual 



' On the Oral and Apical Systems of the Echinoderms, part i., Qxiart. Joum. Micr. Sci., vol. xviii., N. S., pp. 

 367-382. Some disputed points in Echinoderm Morphology, Ibid., vol. xx. pp. 322-329. On the Apical System of the 

 Ophiurids, Ihid., vol. xxiv. pp. 1-22. Vide, Note A. 



2 Oral and Apical Systems, part ii., Ihid., vol. xLx., N. S., pp. 191-193. 



8 See Sirarotli, Zdfschr. f. wiss. Zool., Bd. xxvii. jx 435 ; and also P. H. Carpenter, On the genus Actinometra, 

 with a morphological account of a new species from tlie Pliilippine Islands, Tmns. Linn. Soc. Land. (Zool.), ser. 2, 

 vol. ii. pp. 55, 66, pi. iii. fig. 4. 



