LU CERiN' A RI^ AND TUEIR ALLIES. 41 



their peculiarities have already been nearly exhausted in a former paragraph (59); 

 in fact there is nothing left to be said in regard to their relative position in tiie 

 peduncle, nor in reference to their mode of connection with the other subdivisions 

 of the system, but their structure yet remains to be described. In that is embodied 

 the most singular of all tlieir qualtities. They are in reality, what they appear to 

 be upon suix'rfical examination, cords wliose mass is so deeply furrowed lengthwise 

 that tlicy could almost be said to be groups of four bands -united by one of their 

 edges. The nature of this mode of subdivision of the cords becomes quite clear 

 when they are cut across {figs. 52, 117, r). Here we see the general outline of 

 the periphery, as well as the minor details of the surface in all their fullness. Each 

 cord, it appears, has a sectional outline resembling an obtuse-angled triangle, two 

 of whose sides face away from the axis of the body, and the third and longer one 

 is convex and faces toward tlie axis. It might well be compared to a triangular 

 prism. Its mass is split nearly tlirough to the apex of the triangle, so as to be 

 parted into two divisions of equal size; and each moiety {fig. 117) is again pene- 

 trated by a fissure, which does not extend more than about half way through it, 

 but trends, like the first one, toward the obtuse angle. All of these subdivisions, in 

 fact the whole surface of the cord, is still farther indented by deep flutings which 

 give it the appearance of being finely ribbed {fig. 113). A highly magnified view 

 of a transverse section of one of these fluted divisions {fig. 117) presents the aspect 

 of a deeply lobed triangular mass. Thus it is that the prismatic cord imitates, in 

 a more concentrated form, the deeply ridged nuiscular layer of the umbella; the 

 idea is the same in both, but here it is carried out to the extreme, apparently serving 

 to increase the surface of contact between it, the moving agent, and the gelatiniform 

 mass (c') about it. At the posterior truncate end the furrows terminate, for the 

 most part, abruptly ; but a few follow it beyond that, along the course of the 

 gradually narrowing muscle, as it bends at a right angle {fig. 4G), and comes to 

 a point in the middle of the adherent disk {figs. 19, 46, r-r). And so it is at 

 the anterior end of the cord, where it gradually decreases in diameter {fig. 47*, ;•■) 

 until it penetrates the chondromyoplax, and then rapidly expands, in the umbella, 

 into a fiat mass, the opsomyoplax (m*). There we find the transition from the 

 deeply fiuted condition of the prismatic mass of the cord into that of the heavily 

 ridged and grooved stratum which pervades the area on each side of the partitions. 

 The greater diameter of the cords is about equal to the shorter diameter of the 

 pedicellar cameras, and from one-third to one-half the breadth of the space between 

 the latter. We have already stated that they are completely imbedded in the 

 chondrophys, but the precise relation which they hold to the decussating fibres of 

 that mass is yet to be illustrated ; and, since that would involve a description of 

 the minutest structure of the gelatiniform column, we -must postpone the subject 

 to the chapter on histology (198, § 25). 



§ 12. The Tentacles. 



<S9. Basis of Attaclment. — The tentacles {figs. 1 7, 22, 54, <^) to (//) are nothing 

 more nor less than hollow cylindrical protrusions of the anterior parietes of the 



April, 1877. 



