. Contributions to the natural history of the United States of America. Zoology; Chelonia (Genus); Ctenophora; Cnidaria; Animals. Chap. III. GENUS PLEUROBRACHIA. 235 {Fig. 15 (f), two chymiferous tiiljes (cc a a" a") run parallel; leaving between them, along the median line, a thick ridge {Fig. 15 y), which is nearly as broad as the diameter of the tubes. The relations of these parts, as seen in profile, may be better understood by referring to the annexed wood-cut {Fig. 87) and the ac- companying explanation, at the same time comparing it with PI. IP. Fig. 15, which is lettered corr
. Contributions to the natural history of the United States of America. Zoology; Chelonia (Genus); Ctenophora; Cnidaria; Animals. Chap. III. GENUS PLEUROBRACHIA. 235 {Fig. 15 (f), two chymiferous tiiljes (cc a a" a") run parallel; leaving between them, along the median line, a thick ridge {Fig. 15 y), which is nearly as broad as the diameter of the tubes. The relations of these parts, as seen in profile, may be better understood by referring to the annexed wood-cut {Fig. 87) and the ac- companying explanation, at the same time comparing it with PI. IP. Fig. 15, which is lettered correspondingly. The thick- ness of the disk as a whole is equal to about two thirds of the breadth, but it thins out at the actinal end,(;'") in just about the same proportion that it. narrows; whereas at the other extremity {(i'"), where it is slightly narrowed, it is thickest, and also terminates ⢠abruptly â directly opposite the junction of the main chymiferous trunk {q) with the two par- allel tulles {a a a") just mentioned. It seems appropriate to compare the shape and proportions of this disk to a flat-soled, broad shoe-last. The structural details of this organ appear very simple, when once fully understood ; but, owing to the fact that it is situated at the bottom of a deep socket {j f f-) and as if plunged into the midst of other organs, Longitudinal section of the J. o o 7 tentacular apparatus of Pleuro- it seems to be quite complicated. Only imagine the socket brachia khododactvla, .4-/.1 to be removed or reverted, as oftentimes does happen in a great measure, and the whole apparatus will , appear like a peripheric ridge, which, at one point, is drawn out into a slender thread, the tentacle. The hn,se {Fig. 15 g g^ g"^) of the tentacle has the form of a high, narrow ridge or keel {Fig. 15 g^ g^ and Fig. 87 /), more or less plicated or distorted, according to whether the apparatus is extended or retracted; but we have never seen it projecting bey
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