582 



AMPHIBIA. 



In later stages (larvae of 7 — 10 mm.) the anterior segmental 

 tubes gradually lose their attachment to the peritoneal epithelium. 

 The extremity near the peritoneal epithelium forms a Malpighian 

 body, and the other end unites with the segmental duct. At a still 

 later stage Avide peritoneal funnels are established, for at any rate a 

 considerable number of the tubes, leading from the body cavity 

 to the Malpighian bodies. These funnels have been noticed by 

 Fiirbringer, Salensky and myself, but their mode of development 

 has not, so far as I know, been made out. The funnels appear to be 

 no longer present in the adult. The development of the Miillerian 

 ducts has not been worked out. 



Dipnoi. The excretory system of the Dipnoi is only known in the 



ailult, but though in some re- 

 spects intermediate in character 

 ))etween that of the Ganoidei 



I , ^_ g™, , ^ , ^r/TJo and Amphibia, it resembles that 



' sst^^r ^^ j.|^g Ganoidei in the important 



feature of the Miillerian ducts 

 { \ ( ^B^^-\ serving as genital ducts in both 



""^ ^^--■" -x sexes. 



/jrn 



Amphibia. In Amphibia 

 (Gotte, Fiirbringer) the de- 

 velopment of the excretory 

 system commences, as in Tele- 

 ostei, by the formation of the 

 segmental duct from a groove 

 formed by a fold of the somatic 

 layer of the peritoneal epithe- 

 lium, near the dorsal border of 

 the body cavity (fig. 399, u). 

 The anterior end of the groove 

 is placed immediately behind 

 the branchial region. Its pos- 

 terior part soon becomes con- 

 verted into a canal by a con- 

 striction which commences a 

 short way from the front end 

 of the groove, and thence ex- 

 tends backwards. This canal 

 at first ends blindly close to 

 the cloaca, into which however 

 it soon opens. 



The anterior open part of the groove in front of the constriction 

 (fig. 399, u) becomes differentiated into a longitudinal duct, which 

 remains in open communication with the body cavity by two (many 

 Urodela) three (many Anura) or four (Coeciliidai) canals. This con- 

 stitutes the dorsal part of the pronephros. The ventral part of the 



Fig. 398. Transvebse section xhkough 

 the region of the stomach of a lakva of 

 acipenser 5 mm. in length. 



St. epithelium of stomach; yk. yolk; cli. 

 notochord, below which is a subnotocliordal 

 rod; pr.n. pronephros; ao. aorta; mp, muscle- 

 plate formed of large cells, the outer parts of 

 which are differentiated into contractile fibres ; 

 np.c. spinal cord ; h.c. body cavity. 



