. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. io8 MANUAL OF ZOOLOGY. one specimen to be seven feet in diameter, with tentacles more than fifty feet in length, the fixed Lucernaroid from which it was produced not being more than half an inch in height. As regards the special structure of these gigantic reproductive bodies, con- siderable differences obtain between the Rhizostomidcs and that section of the Pelagidce in which this method of reproduction is employed. In the Pelagidce, namely, the generative zooids possess a gene
. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. io8 MANUAL OF ZOOLOGY. one specimen to be seven feet in diameter, with tentacles more than fifty feet in length, the fixed Lucernaroid from which it was produced not being more than half an inch in height. As regards the special structure of these gigantic reproductive bodies, con- siderable differences obtain between the Rhizostomidcs and that section of the Pelagidce in which this method of reproduction is employed. In the Pelagidce, namely, the generative zooids possess a general, though chiefly mimetic, re- semblance both to the genuine Discophora and to the free-swimming medusi- form gonophores of so many of the Hydrozoa, and they have the following structure. Each (fig. 25) consists of a bell-shaped, gelatinous disc, the "um- brella," from the roof of which is suspended a large polypite, the lips of which are ex- tended into lobed processes often of considerable length, " the folds of which serve as temporary receptacles for the ova in the earlier stages of their ; The polypite— manubrium or proboscis—is hollowed into a digestive sac, which communicates with a cavity in the roof of the umbrella, from which arise a series of radiating canals, the so-called "chylaqueous ; These canals, which are never less than eight in number, branch freely and anastomose as they pass towards the periphery of the umbrella, where the entire series is connected by a circular marginal canal. This, in turn, sends tubular processes into the marginal tentacles, which are often of great length. Besides the tentacles, the margin of the umbrella is furnished with a series of peculiar bodies, termed " lithocysts," each of which is protected by a sort of process or hood derived from the ectoderm, and consists essentially of a combined "vesicle" and " pigment-spot," such as have been described
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Keywords: ., bookauthorni, bookcentury1800, bookdecade1870, booksubjectzoology
