DEVELOPMENT OF ANTEDON (COMATULA, LAMK.) EOSACEUS. 715 



canals ; whilst each of the five spout-like rays joins the intermediate portion of one of the 

 Eadials, tlie inflected margins of the former being applied to the borders of the vertical 

 furrow of the latter, in such a manner that the two grooves are united into a complete 

 canal (b, b). Notwithstanding the apparent continuity between the calcareous reticula- 

 tion of the Rosette and that of the Pentagonal Base at the extremity of each ray of the 

 former, I am disposed to think the continuity not real, since, after boiling in a solution 

 of potass, the rosette separates itself from the Radials without any positive fracture 

 at these points. A real continuity, however, would seem to exist between the central 

 prolongations of the first lladials (§ 33) and the discoidal portion of the rosette, these 

 prolongations attaching themselves to it either separately, or after coalescing with each 

 other either to a slight extent or so completely as to form the collar just described, 

 and the junction being so complete that its separation can only be effected by fracture. 



36. This " Rosette," when viewed only with reference to its own structure and its con- 

 nexions with the surrounding base of the Calyx, is one of the most beautiful objects 

 with which I am acquainted. But the interest attaching to it will be found greatly 

 heightened, when the extraordinary process by which it is developed from the original 

 Basals of the Pentacrinoid larva shall have been explained (^^ 89, 90) ; still more, when 

 its relations to the soft parts lodged in the Centro-dorsal cavity and its Radial Canals 

 shall have been displayed in the Second Part of this Memoir. 



37. Second Eadials. — Proceeding now to the other components of the Calyx, we find 

 the Second Radial (Plate XXXVI. fig. 2) to be a someAvhat discoidal plate of elliptic 

 figure, having two nearly parallel faces, one internal or central, articulating with the 

 First radial, the other external or distal, articulating with the Third radial. The 

 internal face (a) is divided transversely (like the external face of the first radial) by a 

 prominent ridge {a, a) that also passes round the large oval opening of the radial canal, 

 and is then continued on either side of the median line to the upper margin of the plate, 

 the two approximated ridges having a furrow between them. The large depressed 

 spaces bounded by these ridges on either side, are again marked out by secondary ridges 

 into two pairs of fossa? corresponding with those on the external face of the first radial 

 (§ 33). Of these the upper pair {c, c) are the deeper, and are for the most part bounded 

 by a pair of thin lamellae extended upwards from the proper margin of the plate, as is 

 obvious when we examine it from the distal side (b, d, d). These lamella; give attach- 

 ment to the distal ends of the flexor muscles ; while in the shallower fosste (a, b, b) are 

 lodged the interarticular ligaments. Beneath the great transverse ridge is a broad fossa 

 (/■) that is particularly deep just beneath the opening of the radial canal {e) ; this gives 

 attachment to the elastic ligament, the tension of which antagonizes the flexor action of 

 the muscles. The external or distal face (b) is divided by a vertical ridge («, a) that 

 passes round the opening of the radial canal, into a pair of lateral fossa? {b, b), which 

 give attachment to the interarticular ligaments that connect the second with the third 

 radial, no muscular bands being here interposed. 



38. Third Eadials. — The Third Radial, when looked-at from above or from below 



