Glass 3. Amphibia. 401 



In the larval Urodeles that pai-t (4 Fig. 328 A) of the foui-th ai-terial arch 

 which lies between the ventral aorta and the point of origin of the pulmonary 

 artery is much narrower than the pulmonary, whilst the rest (4') of this arterial 

 arch is as wide as the latter : the pulmonary artery in the larva evidently 

 receives direct the chief mass of the blood from the vessel formed by the 

 imion of the three efferent branchial arteries, i.e., arterial blood. In the adult 

 the relative sizes of the different sections of the foui-th arterial arch are 

 exactly reversed (Fig. 328 B). 



In the larvsB generally the circulation is essentially piscine. In the 

 adult, in spite of the single ventricle, the arterial blood from the lungs is to 

 some extent separated from the venous blood ; the an'angements are, however, 

 too complicated to be more closely gone into here. SuflB.ce it to say that by 

 means of the spiral valve of the conus almost all the Sirterial blood from the 

 left auricle flows into the first two paii's of arterial arches, whilst the venous 

 blood from the right auricle goes partly into these, partly into the third and 

 foui-th pairs ; the fourth pair, as ah-eady mentioned, gives rise to the pulmonaiy 

 arteries, which receive entirely venous blood, whilst that in the systemics is 

 " mixed." 



From the fourth ai-terial arch, larger or smaller branches go to the skin; in 

 the Anura especially, there is a vei-y large cutaneous arteiy, which thei'efore 

 can-ies venous blood ; and as a matter of fact, the sMn is hei-e of great respira- 

 tory importance ; but the blood thus oxydised, mixes with that of the other 

 veins, and goes to the right auricle. On the whole, the separation is very 

 incomplete. 



The ureters open into the cloaca^ which has a ventral outgrowth 

 serving as a urinary bladder. The latter, which is often 

 drawn out into two points, is not directly connected with the ureters, 

 but opens separately into the cloaca. 



The ovaries vary in size, according to the time of year ; in 

 the breeding season they are very large. The Miillerian ducts 

 are long, coiled tubes, which are thickest at the breeding season, 

 on account of the great development of the albumen glands lying in 

 their walls ; tbey open into the abdomen by funnels, situated quite 

 anteriorly, and far distant from the ovaries ; the ripe ova are wafted 

 to the funnels by movements of the cilia upon a portion of the 

 abdominal epithelium; they usually open separately into the cloaca 

 by their other ends. In the Anura, the hinder portion of the oviduct 

 is expanded into a vesicle, which is filled with ova at spawning time. 

 The testes (Pig. 288), are connected with the urinary tubules of the 

 anterior end of the kidney, which, in the Urodela is smaller than 

 the posterior end, and the spermatozoa pass out through the ureter ; 

 the duct of the anterior portion of the kidney is, moreover, in many 

 cases, almost completely separated from the other renal ducts with 

 which it unites only just before the common opening into the cloaca. 

 In the males, there is a rudimentary Miillerian duct on each side. 



Actual copulation takes place only in the Gymnophiona; 

 the eversible cloaca of the male serving as an intromittent organ. 

 In the Anura, the male clasps the female with the fore limbs, and as 

 the eggs leave the cloaca, pours the sperm over them; fertilisation 



D D 



