518 CHORD ATA 



arterial trunk is, at least externally, single. The arterial arches show 

 different relations and have different fates. With branchial respiration 

 the first three afferent and efferent arteries are connected in two ways, 

 the one by the capillaries of the gills, the other direct (fig. 569, b). In the 

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

 off the pulmonary arteries (/>) to the lungs (compare also fig. 537,77). 



With the loss of gills (fig. 570) the third arch frequently disappears 

 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 (r) supplying the head, the second unites with its fellow of the 

 opposite side to form the dorsal aorta; the fourth forms the pulmonary 

 artery, and in the Anura, gives off a cutaneous artery (cu) to the skin. A 

 longitudinal 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 a separation of pulmonary and systemic cir- 

 culations, although the blood all passes through a common ventricle. In the 

 urodeles the primitive part of the last arch, connecting the pulmonary 

 artery with the dorsal aorta, may persist as a duct us Botalli. 



The sexual organs (fig. 539) are similar to those of selachians. The 

 eggs pass from the ovary to the oviducts (Muller'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 distinction 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 colored structures, best developed between the repro- 

 ductive 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 arc oviparous, but occasionally, a,s Salamandra maculosa and 5. atra 

 of Kurnpc, viviparous species occur. The male of Alytes obstetr leans wraps 

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

 while the females of Ampliiuma and Ichtliyophis watch over the eggs. The 

 male of Rhinoderma dnricinii has a large sac arising from the pharynx in which 

 the ei^s and young are cared for until the completion of the metamorphosis. 

 In Pi pa 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. 



