Chap. III. GENUS BOLINA. 257 



almost straight to their termination, while those of the lateral ambulacra are arched 

 over the two rounded parallel ridges which inclose the circumscribed area. It is 

 easily ascertained, that eight narrow bands, similar to those observed in Pleuro- 

 brachia, extend beyond the extremity of the ambulacra toward the central black 

 speck, or rather toward the bulb under it, and that they are the prolongation of 

 the vertical rows of locomotive flappers. Along the sides of the body the rows 

 of locomotive flappers also gradually taper toward their actinal extremity, and, as 

 soon as they reach the height of the dilatation of the lobes, the locomotive combs 

 disappear, and the chymiferous tubes which accompany them can alone be traced 

 fixrther. In the lateral amljulacra, however, the rows of locomotive flappers taper 

 much sooner, and terminate at the base of the small lateral lobes, near their inner 

 margin, for a considerable length above the actinal extremity of the ambulacra of 

 the large lobes. In the small lobes we trace also a narrow prolongation of the 

 chymiferous tubes of the lateral ambulacra, which extend beyond the locomotive 

 fringes. The course of these narrow tubes in the lobes is very difficult to follow, 

 and their connection with each other and with the central chymiferous cavit}' has 

 been entirely overlooked by former observers, with the exception of Milne-Edwards ; ^ 

 though in the figures of Bolina elegans published by Mertens, there are already 

 indications that he noticed the outline of their convolutions. I shall first trace 

 the course of these tubes upon the larger lobes. As long as the tubes follow a 

 straight course in the prolongation of the anterior and posterior aml^ulacra {Fig. 

 92 t), they remain at the surface of the lobes, covered only by the epidermis, 

 beyond the ambulacra! rows themselves. But as soon as 

 they converge towards the lower margin, where they bend 

 to take an inward course, they penetrate deeper into the 

 substance, across the whole thickness of the lobe itself, till 

 they reappear upon its inner surface, where they are nearest 

 to each other ; they then rise again, diverging toward the 

 sides and following almost exactly the outline of the lateral 

 margins of the lobes, along which they ascend In) toward ^ *"■ , 



o 7 o •/ \ / Bolina alata, Ag. 



their bases, rising even higher than the lower termination (Seen from the narrow side.) 

 of the ambulacral combs, indeed nearly as high as the leases of the auricles ; they 

 then converge again, bend downward, and in a sinuous, winding course {x) 

 descend a second time toward the middle of the lobe, to rise and converge again, 

 and then descend for the third time, in a parallel course, to nearly the same 

 level with their first bend, and, converging once more from the two sides, unite 

 (*) in the medial line of the lobe : so that there is a direct commmiication 



^ Milne-Edwards, Eeelierclies, etc. Aiin. Sc. Nat. 2de ser., vol. 16, p. 203, PI. 3. 

 VOL. III. 33 



