. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. CCELENTERATA : HYDROZOA. I OS able rapidity by means of the alternate contraction and expan- sion of the umbrella. Around the margin of the umbrella are tufts of short tentacular processes, and in its centre is a poly- pite with a quadrangular, four-lobed mouth. " In transverse section the polypite tnay be. described as some- what quadrilateral, with a sinuous out- line, which expands at its four angles to form as many deep longitudinal folds, within which the simple genera-
. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. CCELENTERATA : HYDROZOA. I OS able rapidity by means of the alternate contraction and expan- sion of the umbrella. Around the margin of the umbrella are tufts of short tentacular processes, and in its centre is a poly- pite with a quadrangular, four-lobed mouth. " In transverse section the polypite tnay be. described as some- what quadrilateral, with a sinuous out- line, which expands at its four angles to form as many deep longitudinal folds, within which the simple genera- tive bands are ; — (Greene.) Wide longitudinal canals are formed by septa passing from the walls of the polypite to the inner surface of the cup, and a circular canal runs immediately beneath the insertion of the tentacles. The reproductive elements are pro- duced within the body of Lucernaria itself, without the intervention of any generative zooid. Order II. Pelagid^.—This order is defined as including Lucernarida which possess a single polypite only, and an umbrella with marginal tentacles. The reproductive elements " are developed in a free U7nbrella, which either consti- tutes the primitive hydrosoma, or is pro- duced by fission from an attached Liuer- ;—(Greene.) Two types, therefore, exist in the Felagidte. The one type is represented by a fixed " trophosome," resembling Lucernaria, but distinguished from it by the fact that the generative ele- ments are not developed in the primitive hydrosoma, but in a free "gonosome," which is produced for the purpose. The second type, represented by Pelagia itself, is permanently free, thereby differing from Lucernaria, which it approaches, on the other hand, in the fact that its generative elements are pro- duced in its own umbrella without the intervention of free generative zooids. Pelagia, however, differs considerably in structure from Lucernaria, and in all essential chara
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Keywords: ., bookauthorni, bookcentury1800, bookdecade1870, booksubjectzoology
