2 THE VOYAGE OF H.M.S. CHALLENGER. 
Pl. LVIIL figs. 1, 3—az; Pl. 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 
Psolidee, and possibly also with the five actinal plates of Paleostoma 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; Pl. XVII. figs. 6-10; Pl. XXVI. figs. 1,2; Pl. XXXII. figs. 6,7; 
Pl, XLT hes: 4.°12=145 Pl XLII fig. 33 Pl XLVIT tes. 10-13% PEW tips, 2,2) 
Pls. LIV., LV.; Pl. LVII. fig. 3, an; Pl. LXII-). The radial skeleton, however, consists 
of successive jomts and rods which are developed in a longitudinal direction, and are 
united to one another by articulation or suture. In either case the ultimate union of the 
two joints is effected 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. VIIb. 
figs. 1, 8, , Id. Pl. XXIV. figs. 6,7; Pl. LVIIL. figs. 1-3—1, lb, ZL). 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 radials of the Comatulee 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 Pentacrinidz and the basals on which they rest, as well as between the five individual 
1 On the Oral and Apical Systems of the Echinoderms, part i., Quart. Journ. Micr. Scz., vol. xviii., N. S., pp. 
367-382. Some disputed points in Echinoderm Morphology, Ibid., vol. xx. pp. 322-3829. On the Apical System of the 
Ophiurids, Ibid., vol. xxiv. pp. 1-22. Vide, Note A. 
2 Oral and Apical Systems, part ii., [bid., vol. xix., N. S., pp. 191-193. 
3 See Simroth, Zettschr. f. wiss. Zool.. Bd. xxvii. p. 485; and also P. H. Carpenter, On the genus Actinometra, 
with a morphological account of a new species from the Philippine Islands, Trans. Linn. Soc. Lond. (Zool.), ser, 2, 
vol, ii. pp. 55, 56, pl. iii. fig. 4, 
