DEVELOPMENT OF ANTEDON (COMATULA, LAMK.) EOSACETJS, 693 



which is covered only by the membranous Perisome. The centre of the visceral disk is 

 occupied by the Mouth (Plate XXXII. fig. 3, m), which is small and slightly prolonged 

 into five angles ; and is surrounded by five somewhat elevated valvular folds, beneath 

 the free edge of each of which is to be seen a row of minute tentacula. From the 

 mouth there radiate five furrows channelled out in the perisome, and having elevated 

 borders scolloped so as to form a series of minute valvules, from beneath each of which 

 issues a cluster of tliree tentacles ; these furrows soon bifurcate, and thus ten furrows are 

 formed, of which one is continued on to the ventral surface of each of the arm^ in the 

 extension of the perisome which clothes it. In the space between two of these furrows 

 we see the large projecting vent or Anus (a), the shape of which diflfers much according 

 as it is full or empty ; sometimes its aperture is so completely closed as to be scarcely 

 discernible, though the tube below is widely distended ; whilst in other states we find 

 the aperture patent, its edges everted and crenate, and the tube leading to it quite shrunk 

 and flaccid. — On looking at the dorsal or aboral face of the central disk, which in the 

 living state is ordinarily the inferior, we find it in great part concealed by an assemblage 

 of jointed and uncinate Cirrhi, radiating from a central tubercle to which they are arti- 

 culated (Plate XXXII. fig. 4), and extending even beyond the margin of the disk : the 

 number of these ordinarily ranges in a full-grown specimen between twenty and thirty- 

 two ; and each of them normally consists of about sixteen segments. When these have 

 been removed, we find the under surface of the calyx to be composed, as shown in 

 Plate XXXII. fig. 1, of a single convex Centro- dorsal plate (c), having a somewhat 

 pentagonal margin, within which are two or more rows of sockets for the articulation 

 of the cirrhi, whilst the central space, which bears no cin-hi, is somewhat flattened. 

 Along the five sides of this pentagon we see five pieces (r^) having their proximal 

 and distal margins nearly parallel, but their surfaces convex ; these are the Second 

 Radials, the First being entirely concealed by the Centro-dorsal. And to the distal 

 margins of the second radials are attached five pieces (r^) of nearly triangular form ; 

 their basal margins rather exceeding in length the distal margins of the second radials 

 to which they are applied ; whilst each of their inclined sides bears the first segment (ir') 

 of an Arm : these triangular pieces are the Third or Axillary Radials. The spaces 

 between the diverging Radials, and between the basal segments of the Arms as far as 

 the fourth, are filled up by the membranous Perisome, which thus completes the floor 

 of the calyx. Sometimes, however, we find minute plates imbedded in the substance 

 of the perisome, at the angles between the second radials (§ 9). 



2. Each Arm is composed of a long series of calcareous segments, of which the dorsal 

 surface is exposed like the dorsal surface of the calyx, whilst the ventral surface is 

 clothed with an extension of the ventral perisome, carrying with it an extension of the 

 radial furrows and their tentacular apparatus. With certain exceptions, hereafter to be 

 noticed, every segment of the arms bears a jointed Pinnule, which repeats on a smaller 

 scale the same structural features; and the furrows which pass from the disk to the 

 arms, send branches also from the arms to the pinnules, which are continued to their 



