GENERATIVE ORGANS OF VERTEBRATA. 



621 



in which, and the extent to which, the chorion is connected with the 

 raucous 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, p), 

 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 (<jl). 



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 Ratitse, and 

 in the Penelopiche 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 

 portion of the organ is retracted by an elastic ligament. 



Another form is seen in the Chelonii and Crocodilini, and in 

 Struthio ; this is distinguished from the previous one by the fact 

 that it is not protrusible. This organ is likewise supported by two 

 fibrous bodies, which are intimately connected together, and covered 

 by mucous membrane (Fig. 349, p). On the dorsal surface there is 

 a groove between the two bodies (s), which appear to be invested by 

 cavernous tissue, at the root in the Crocodilini and Chelonii, and 

 along the whole length in Struthio. As this tissue is more abundant 

 at the anterior end of the fibrous bodies (in Struthio it is formed 

 from the continuation forward of a third elastic body, which is 



Pig. 355. Cloaca of 

 Py t h o n, opened from 

 in front. R Hind- 

 gut, u Orifices of the 

 ureters, gl Glands, 

 which open at *. 

 2~> Penial tubes, ono 

 of which is laid open 

 longitudinally. 



