244 



ANATOMY OF VERTEBRATES. 



119 



cloaca, both in extent and in tlie diameter of the tube composing 

 them ; and they are so closely compacted, and inclosed by a cover- 

 ing of peritoneum, as to present 

 in a longitudinal section the ap- 

 pearance of a series of cells, 

 which are capable of retaining, 

 as in a vesicula seminalis, a 

 quantity of the seminal secre- 

 tion. In the Sparrow there is a 

 dilatation at the end of each 

 vas deferens, which opens, as in 

 the Common Cock, on a papilla, 

 situated in the urogenital divi- 

 sion of the cloaca anterior to 

 the insertion of the ureter. 



The base of each papilla is 

 surrounded by a remarkable 

 plexus of arteries and veins, 

 M, M, fig. 94, which serve as an 

 erectile organ during the vene- 

 real orgasm, when the fossa of the 

 turgid papilla is everted, and the 

 semen brought into contact with 

 the similarly everted orifice of 

 the oviduct in the female, along 

 which the spermatozoa pass by 

 undulatory movements of their 

 ciliary appendage or ^ tail.' 



In some Natatores which co- 

 pulate in water there is pro- 

 vision for a more efficient coitus 

 than by simple contact of evert- 

 ed cloaca3, and in the Anatidce 

 a long single penis is developed, 

 fig. 119. It is essentially a 

 saccular production of a highly 

 vascular part of the lining mem- 

 brane of the cloaca, continued 

 from the fore-part of that cavity, 

 ib. a, a ; and in the passive state 

 is coiled up like a screw by the 

 elasticity of associated ligamen- 

 The vascular membrane gives oiF many small 



Penis of a Drake, xxvii 



tons structure, h, h. 



