ORGANS OF GENERATION. 179 



glandular layer, which surrounds the cloaca, and forms a protuberance 

 around the anus, which consists of several layers of cosca, and pro- 

 jects very much at the time of the coitus. 



The Lizards and Serpents possess a double penis capable of being 

 everted ; these two intromittent organs are in the Serpents often 

 very long, slender and pointed, and are here, frequently like other 

 organs, c. g., Coluber natrix, asymmetrically developed, the left be- 

 ing the longest. They lie extended beneath the integument in a 

 cavity behind the anus at the commencement of the tail, and can 

 be everted from the cloaca, as in the Ducks and Geese, by a pair of 

 special muscles ; they are devoid, however, of elastic tissue and a 

 fibrous body. At the season of the coitus they form, when everted, 

 a double tube, which serves for the exit of the semen. Frequently, 

 as in the Vipers and Rattlesnakes, and also in Python, each of the 

 two penes is bifurcated at the extremity. 



The penis is single in the Tortoises and Crocodiles, and resem- 

 bles more that of the Two-toed Ostrich among Birds ; it consists of 

 a fibrous body, and has a groove upon its upper and anterior sur- 

 face, which is imbedded in cavernous tissue, and into which the 

 seminal fluid is received from the seminal ducts. In front we find 

 a glans of varied form, infundibuliform in the Crocodiles, and very 

 largely developed in the Tortoises ; the whole of it consists, as in 

 Man and Mammalia, of cavernous tissue. A muscle serves to draw 

 the penis out of the cloaca. It is peculiar to all Reptiles, that the 

 urogenital orifice lies invariably, as in the higher Vertebrata, in front 

 of the anus. 



In the males and females of the Tortoises and Crocodiles, there is 

 found what are called the Peritoneal canals, which conduct as mem- 

 branous tubes or slits from the peritoneal cavity into the cloaca, 

 and are continued upon the penis as far as the glans, and there ter- 

 minate blindly ; in the female they are to be traced to the root of the 

 clitoris ; in both sexes they remind us of the vaginal canals of the 

 Mammalia (see p. 54), and are probably the remnent of a foetal struc- 

 ture, viz., the excretory ducts of what are called the false kidneys or 

 Wollfian bodies. 



The two sub-classes of Reptiles, differing, as we have already 

 seen, in so many important particulars from each other, are also 

 developed from the ovum in an entirely different manner. The 

 Naked Amphibia agree with Fishes in having neither amnion nor 

 allantois,both of which foetal structures occur, however, in the Squami- 

 gera, of whom many have proposed to form a distinct class, limit- 



