ir. VERTEBRATA: AMPHIBIA. 585 



caiiilliiries of the gills, the other direct (fig. G15, i). In the fourth 

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

 oft' the pulmonary arteries (p) to the lungs. 



With the loss of gills (fig. 016) the third arch frequently dis- 

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

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

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

 soco]id 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 (cu) 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 tlie 

 skin, wliile the blood returned from the lu]igs 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 

 l)lood all j)asses 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- 

 ticju from tlie 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 sexnal 

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

 ored structures, best developed between the reproductive seasons. 



A sort of ooi)ulation occurs, and internal impregnation is effected in 

 many urodeles and in tfie Gj'muopliiona, but not in tlie Anura. Tlie Anura 

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

 maculosa and 8. atra of Europe, viviparous species occur. Many inter- 

 esting brooding habits are known. The male of Ahjtes ohstetricans \Yraps 

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

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

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

 pljarynx in wliich the eggs and young are cared for until the completion 

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

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

 pHicket, from wliich tlie 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. 



