. Elements of Comparative Anatomy. GENERATIVE OEGANS OF VERTEBRATA. 621 in wliicTij and tlie extent to wticli, the chorion is connected witli the mucous membrane of the uterus, and according to the modifications undergone by the latter organ. § 457. The copulatory organs form another series of parts formed by the differentiation of the wall of the cloaca. In the Selachii, indeed, organs which did not belong to the generative apparatus— parts of the hinder appendages—are used as organs of copulation and modified accordingly, but new organs begin to be differentiated, which in the Amphibia are f
. Elements of Comparative Anatomy. GENERATIVE OEGANS OF VERTEBRATA. 621 in wliicTij and tlie extent to wticli, the chorion is connected witli the mucous membrane of the uterus, and according to the modifications undergone by the latter organ. § 457. The copulatory organs form another series of parts formed by the differentiation of the wall of the cloaca. In the Selachii, indeed, organs which did not belong to the generative apparatus— parts of the hinder appendages—are used as organs of copulation and modified accordingly, but new organs begin to be differentiated, which in the Amphibia are faintly indicated by the presence of a papilla which projects into the cloaca. These belong to one of two typical forms ; in one the organs are connected with the posterior, and in the other with the anterior wall of the cloaca. One of them is dominant in the Saurii and Ophidii. The copu- latory organs first appear as external appendages, placed just behind the cloaca ; later on these are invaginated in a tubular fashion (Fig. 355, j)), and are only protruded during copulation. When protruded, each of these organs is continued into two more or less blunt ends, which vary in form. At the sides there is a groove, which is continued on from the cloaca, and which has a spiral course posteriorly, and is then directed towards the middle line; this serves to convey the sperm. The largest of the muscles supplied to it are the retractors, which are inserted into the blind end of the tubes. Glands open near the root of the tubes (gl). The second form contains a number of dif- ferent structures, all of which, however, pro- ceed from the anterior wall of the cloaca, and must be regarded as modifications of one and the same arrangement. One form of these organs is found in most of the Ratit», and in the Penelopidae and Natatores (Anser). It consists of a tube which is supported by two fibrous bodies, and which, when pro- truded, forms a groove which leads from the cloaca. The terminal
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