328 CLASS REPTILIA. 



They correspond to the posterior thick part of the amphibian 

 kidney. The ureter, which is to be regarded as the united 

 collecting tubes of the metanephros of Amphibia, opens into the 

 cloaca, and the urine is often a whitish mass of firm consistency 

 containing a considerable quantity of uric acid. There is a 

 bladder in Lacertilia and Chelonia. 



In the reproductive organs the mesonephros of Amphibia 

 and its duct have become entirely taken over into the service of 

 the testis. The mesonephros (wolfFian body) has lost its kidney 

 structure and become incorporated into the testis as a portion 

 of the epididymis, while the mesonephric duct (pronephric, 

 primitive longitudinal duct) forms the rest of the epididymis 

 and vas deferens. In the female the mesonephros and its duct 

 atrophy or persist as a small vestige (Rosenmiiller's organ, canal 

 of Gaertner), and the duct of Miiller persists as the oviduct. 

 The oviducts begin with a wide abdominal ostium, have a 

 sinuous course and glandular walls, and open into the cloaca. 



The eggs are large and much distended with yolk as in birds. 

 They are fertilized in the oviduct and receive a coating of 

 albumen and a shell (membranous or calcareous) in their passage 

 down the latter. They are usually laid as soon as the shell is 

 formed and undergo the greater part of their development out- 

 side the mother, who as a rule takes no further trouble about 

 their fate, but in a few forms they are retained for a considerable 

 time in the oviduct, sometimes till the embryonic development 

 is completed. 



The males always possess organs of copulation, to which 

 similarly arranged but smaller structures (clitoris] correspond in 

 the female. In snakes and lizards these organs are paired and 

 consist of protrusible hollow pockets of the cloaca. When pro- 

 truded their surface is traversed by a groove which conveys the 

 sperm from the genital openings in the cloaca. In Chelonia and 

 Crocodilia, a median erectile penis, consisting of two corpora 

 cavernosa and a terminal glans and supported by fibrous bands, 

 is attached to the ventral wall of the cloaca. 



The developmental history * of reptiles is very similar to that of 



* C. E. v. Baer, Entwickelungsgeschichte der Thiere, II. Konigsberg, 

 1837. H. Rathke, Entwickelungsgeschichte der Natter, Konigsberg, 1839. 

 Id., Die Entwick. der Schildkroten, Braunschweig, 1848. Id., Unters. 

 ub. d. Entwick. u. d. Korperbau der Crocodile, Braunschweig, 1866. L. 

 Agassiz. Embryology of the Turtle, Contributions to the Natural History 

 of the United States, II, Boston, 1857. 



