LUCERNARI^ AND THEIR ALLIES. 39 



of the chondrophys (c) and the equally abrupt concave borders of the chondromyo- 

 plax (A), forming an intervening partition (A-') tliere, and terminates, as just indicated, 

 a few lines above. In such a precise, peculiar manner the umbellar division of this 

 system intervenes between the juxtaposed margins of the two gelatiniform strata 

 at all points in the periphery ; not only along the sinuses of the octagon, but even 

 at the distal side of the bases of the groups of tentacles and the anchors. The 

 modes of approach to this terminus, though, are quite diverse in the several regions 

 mentioned, and are, therefore, to be described separately. 



83. We turn now to the ribbon-like peimations which diverge from the parti- 

 tions. Their internal conformation is best exposed by a section across two of the 

 corners of the octagonal umbella, with an intervening partition {fifj. 61). By this 

 we learn that the bands in question are the expressions of the thinner portions of 

 the muscle which lie between less transparent ridge-like thickenings {rn). The 

 disposition of the ridges is peculiar to tliis region, and differs from that described 

 in the last paragraph, inasmuch as the intervals in the present case are two or three 

 times broader than the ridges. The latter are heavier and plunge deeper into 

 the chondromyoplax than the ridges of the buttresses and the adjoining face of 

 the umbella ; in fact they reach half way or more through the thickness of this 

 gelatiniform layer. We ought to qualify this, hoAvever, by stating that, as the 

 muscle approaches the margin of the umbella, it loses its folds for a short distance, 

 and is as thin and smooth as that portion of it which lies in front of the genitalia, 

 but soon it becomes ridged again, and then joins the marginal band (?«'). One 

 more peculiarity is to be mentioned, and that is to be found along the line of the 

 partitions. Here the muscle attains to its greatest thickness and massiveness, as- 

 suming the form of a broad rib (in*), which is about half as thick as it is wide, and 

 occupies the whole depth of the chondromyoplax, excepting that part of it (/>') 

 which constitutes the mass of the partition. It is not homogeneous, by any means, 

 but on the contrary, as a transverse section shows, it appears to be deeply folded 

 lengthwise ; the folds, where cut across, resembling the ends of so many divided 

 threads. Surveying it in a longitudinal section {fig. 6-i, 7/;;'), the folds evidently 

 run parallel with each other, but not continuously, some fading out while others 

 begin, and all trending in one general direction. At the proximal ends [fig. 47^*, 

 -v/.*) of the partitions, the folds run into the larger condnplications of the muscular 

 cord (?•'-) just as it comes forward from the peduncle and enters the umbella. 



84. The marginal hand of muscle is so strongly marked by its ridges that it 

 appears, at first sight, as if it were a distinct strip, a deeply plaited hem ; but we 

 have already seen (*\ 82) that it is continuous with the neighboring opsomyoplax, 

 and that its condnplicated physiognomy is due to the ridges which project from tlie 

 general mass into the chondromyoplax. When, therefore, we speak of it as the 

 marginal muscle, or band, it must be understood in this light. In the neighbor- 

 hood of the tentacles its ridges disappear, and it then ceases to be recognized as 

 anything more than a thin, uniform stratum (100), indistinguishable from the rest 

 of the muscular layer; while opposite the anchors {fig. 25) it retains a consider- 

 able proportion of its ridges (»;,') ; yet these are variable m ninnber and strength. 

 Tlic true opsomyoplax is strictly confined to the parietes of the umbella, and 



