IV. VERTEBRATA: AMPHIBIA. 585 



capillaries of the gills, the other direct (fig. 615, b). In the fourth 

 arch there is no gill system, but on the other hand this arch gives 

 off the pulmonary arteries (p) to the lungs. 



With the loss of gills (fig. 616) the third arch frequently dis- 

 appears entirely (Anura), as well as the gill circulation of the 

 others, while the direct circulation persists, at least in part. The 

 first arch gives rise to the carotids, supplying the head (c) ; the 

 second unites with its fellow of the opposite side to form the dor- 

 sal aorta; the fourth forms the pulmonary artery and, in the 

 Anura, gives off a cutaneus artery (ou) to the skin. A longitu- 

 dinal fold inside the arterial trunk is so arranged that the venous 

 blood from the body coming to the heart through the right auricle 

 is mostly sent out through the fourth arch to the lungs and the 

 skin, while the blood returned from the lungs by the pulmonary 

 vein passes through the left auricle and then through the first 

 and second arches (carotid and aortic arches). So there is here a 

 separation of pulmonary and systemic circulations, although the 

 blood all passes through a common ventricle. 



The sexual organs (fig. 581) are similar to those of selachians. 

 The eggs pass from the ovary to the oviducts (Miiller's duct), and 

 in this are enveloped with a gelatinous layer. The spermatozoa, 

 on the other hand, pass through the anterior part of the Wolffian 

 body (' kidney') and thence out through the ureter. The distinc- 

 tion from the selachians lies in the fact that a urinary bladder, 

 lying ventrally to the rectum, is present, at some distance from the 

 urinary ducts, which open dorsally into the cloaca. Besides sexual 

 organs fat bodies frequently occur, lobed and often brightly col- 

 ored structures, best developed between the reproductive seasons. 



A sort of copulation occurs, and internal impregnation is effected in 

 many urodeles and in the Gymnophiona, but not in the Anura. The Anura 

 and most other forms are oviparous, but occasionally, as Salamandra 

 maculosa and S. atra of Europe, viviparous species occur. Many inter- 

 esting brooding habits are known. The male of Alytes obstetricans wraps 

 the cords of eggs about his legs and crawls into a hole until the young are 

 hatched, while the females of Amphiuma and Ichthyophis watch over the 

 eggs. The male of Rhinoderma darwinii has a large sac arising from the 

 pharynx in which the eggs and young are cared for until the completion 

 of the metamorphosis. In Pipa americana the male places the eggs on its 

 back, the skin thickening around them so that each lies in a separate 

 pocket, from which the young escape at length in nearly the adult form. 

 In Nototrema and Notodelphys there are dermal sacs upon the back for the 

 reception of the eggs. 



