Page:Scientific results HMS Challenger vol 18 part 2.djvu/871

Rh are placed nearly in one plane and form a hand. The form of the fingers is very variable and most characteristic of the individual species. Very often they have the shape of a human finger, and are smooth, spinulate, or armed with recurved hooks. The distal end of each finger often again bears a small coronet or a spathilla (Pl. 128, figs. 5-9), and sometimes it is arrow-shaped (Pl. 126, fig. 2a). All these apophyses of the terminal coronets as well as the anchor-pencils of the mantle and the finest branches of the tubes, are hollow and filled up by jelly.

The different number and arrangement of the styles offers the best means for the distinction of genera in the Cœlographida. The minimum number is six (Cœlographis, Pl. 126, fig. 1), the maximum number sixteen (Cœlothamnus, Pl. 122, fig. 3, and Cœlagalma, Pl. 126, fig. 4). Since the arrangement of the styles in both valves is constantly symmetrical, the fundamental form of the whole body is in all Cœloplegmida "amphithect," as in the Ctenophora. The longitudinal or main axis of the body is vertical, with two distinct poles; the proboscis of the central capsule and the two rhinocannæ are directed upwards, towards the oral pole; the caudal tube of each valve is directed downwards, towards the aboral pole. The two other axes of the body are unequal, horizontal, and perpendicular one to the other; each has two equal poles. On the poles of the sagittal axis lie the galeæ of the dorsal and ventral valves; on the poles of the frontal axis lie the two secondary openings or parapylae of the central capsule. The frontal fissure or the large cleft between the dorsal and ventral valves of the skeleton lies in the vertical frontal plane of the body, which is perpendicular to the vertical sagittal plane; the equatorial plane, however, is horizontal.

The central capsule of the Cœlographida exhibits the same shape and position as in the preceding Cœlodendrida. It is subspherical, slightly depressed in the direction of the main axis, and lies enclosed between the two central valves of the lattice-shell. Its three constant openings lie in the frontal plane, and therefore in the frontal fissure between the two valves. The astropyle, or the main-opening of the capsule, lies on the oral pole of the main axis, and its radiate operculum (d) is directed upwards; the curved proboscis arising from it (o) is prominent between the mouths of the two opposed rhinocannæ. The two lateral parapylæ or accessory openings lie on both sides of the aboral pole, on the right and left (Pl. 127, figs. 4-6). The large spheroidal or somewhat lenticular nucleus (n) is usually about half as broad as the capsule, and contains numerous nucleoli. The protoplasm around the nucleus contains many vacuoles, and in the oral part of the capsule (between nucleus and operculum) often numerous groups of crystals (Pl. 127, figs. 4-6k, 7). The double membrane of the central capsule exhibits the same shape as in the other.

The calymma, or the extracapsular jelly-veil, is in the Cœlographida very voluminous, and includes the entire skeleton, the fork-thicket of the Cœlotholida, the lattice-mantle of the Cœloplegmida, and also the prominent large styles. Only the distal ends of the