368 COMPARATIVE ANATOMY 



opens separately on a papilla on the dorsal wall of the cloaca. 

 Only in the genera Bufo and Alytes do the two oviducts fuse 

 together into a posterior unpaired canal. 



In female Urodeles a number of tubes serving as a receptaculum seminis 

 may be present in connection with the cloaca, and the male is provided with 

 a cloacal gland which secretes spermatophores. 



After receiving a gelatinous coating from the glands in the wall of the 

 middle part of the oviduct, the eggs of Anurans pass into the dilated portion 

 of the duct, and become united together into irregular masses (Frog) or chains 

 (Toad). 



In Epicrium glutinosum (Gymnophioiia) the eggs are very similar to those 

 of Sauropsida : they are exceptionally large (9 mm. long), of an oval shape, 

 and possess a large yolk. They become coated after fertilisation with a 

 tough albumen in the oviduct, and this becomes drawn out at the poles into 

 chalazse, by means of which the eggs are connected together like the beads of 

 a necklace. The segmentation is meroblastic, and takes place in the oviduct ; 

 and the eggs are laid in the earth, the mother coiling herself round them. 



Fat-bodies (corpora adiposa) are present in all Amphibia in 

 connection with the gonads : they are formed of adenoid substance, 

 fat, and leucocytes, and contain numerous blood-vessels. 



The corpora adipqsa probably have an important physiological (nutritive) 

 relation to the gonads : Amphibians, after remaining for months without food, 

 throughout their winter sleep, are able as soon as spring arrives to give rise 

 to thousands of offspring. 



Reptiles and Birds. The essential differences between the 

 urinogenital organs of the Anamnia and Amniota have already 

 been described (pp. 346, 356, and Fig. 273). a 



In the Sauropsida, as in other Vertebrates, the form of the 

 gonads is influenced by that of the body : thus in Chelonians they 

 are broad, while in Snakes and snake- like Lizards they are more 

 elongated. In the latter cases, as well as in other Lizards, they 

 are asymmetrical, so that the organ of one side is situated more 

 or less in front of that of the other. More room is thus obtained 

 for the development of the ovaries ; and, in cases where the eggs 

 are very large, the organ of one side tends to disappear, as in 

 certain Elasmobranchs (e.g., Scyllium) : in Birds, for instance, the 

 left ovary only is completely developed and functional. 



In Reptiles the ovaries are penetrated by a highly vascular 

 network of trabeculse, and in the lymph-cavities thus formed the 

 formation of ovarian follicles takes place. 



The oviducts (Fig. 294) possess wide funnel-shaped abdominal 

 apertures, and are usually much folded transversely ; the right is 

 often longer than the left. Their walls are provided with numerous 

 muscular elements and glands for the formation of the albumen 

 and egg-shell, and they increase in size in the breeding-season. 

 In Birds the right oviduct, as well as the right ovary, becomes 

 more or less completely degenerated ; the left oviduct is considerably 

 coiled. 



