UROGENITAL ORGANS 365 



cavity, from which they pass into the ostium tubae. The ovarian cavity is 

 lymphatic in character. The oviducts are very long, the ostia far forward, 

 and in the adults they are greatly coiled and have glandular walls which secrete 

 the gelatinous substance which envelops the eggs. The oviducts of the two 

 sides open separately to the cloaca in most species, but in the toad the two unite 

 a little in front of the cloacal opening. 



Fertilization is external in the anura, internal in caecilians and urodeles, 

 though there is no intromittent organ aside from the somewhat protrusible 

 cloacal region, well developed in caecilians. In the urodeles the cloaca has a 

 glandular lining, and in the females it contains tubules which act as reservoirs of 

 sperm. In the male the glands secrete a substance which binds the spermatozoa 

 into bundles (spermatophores). 



There are many interesting accessory reproductive relations among the 

 amphibia. Thus the caecilians and Amphiuma lay their eggs in long strings in 

 the soil and the female incubates them. The male often takes charge of the 

 eggs. In Pipa each egg undergoes development in a pit in the skin of the back 

 of the female, and in Notoirema and Opisthodelphys (South American tree-toads) 

 there is a large pocket in the skin of the back, opening near the coccyx, where 

 the eggs are carried until partially (Notoirema) or entirely developed. Sala- 

 mandra maculosa and S. atra bring forth living young, the former being born 

 with gills, the latter in the perfect condition. Oviposition usually occurs in 

 the spring in colder climates (in the autumn with Cryptobranchus of America) 

 and as the drain on the system is very considerable immediately after hiberna- 

 tion, the substance of the fat body, which always is closely connected with the 

 gonads, is utilized at this time. 



SAUROPSIDA. — Reptiles and birds agree, in the general features -of the 

 urogenital apparatus with the amniote conditions as outlined in the general 

 account above. The pronephros is rudimentary at all stages and at no time 

 functions as an excretory organ. The mesonephros (which always lacks nephro- 

 stomes) takes its place in foetal life, and in some reptiles it continues to function 

 for some time after hatching, but in all it is eventually replaced by the meta- 

 nephros, though its degenerate remains persist in the reptiles (better preserved 

 in the female) as the so-called 'yellow body.' Another portion persists in 

 the male, forming, much as in mammals, the connexion between the testis and 

 the vas deferens. As long as the mesonephros remains functional, the Wolffian 

 duct is the urinary passage, but after the metanephros comes into function, the 

 duct degenerates in the female, though persisting as the vas deferens in the male. 

 It opens either into the urinary bladder or into the cloaca. 



The metanephros never extends as far forward as does the mesonephros of 

 the ichthyopsida, but is usually restricted to the posterior part of the body 

 cavity and frequently to the pelvic region. It is usually small and compact or 

 lobulated, but in the snakes it is long, and the lobulation is sometimes so exten- 

 sive that the lobules are connected only by the ureter. In the lizards and some 

 song birds, the kidneys of the two sides are often connected by a cross band 

 behind. The mesonephroi of birds arc usually three-lobed, the lobules lying 

 in cavities in the pelvis between the sacral vertebrae and the transverse processes. 

 The waste is carried from the kidneys by the ureters which open sepa- 



