252 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. 



n. 



B 





nc 



Fig. 136. — Transverse sections showing 

 various stages in the development of 

 the opisthonephros. (After Furbringer, 

 ■ 1877.) 



A, Triton alpestris ; B, Salamandra maculata, 

 14 mm. ; C, D, Salamandra maculata, 17 mm. ; 

 JE, SalamandranuKulata, 21 mm. ; F, Salamandra 

 m,aculata, 25 mm. A, dorsal aorta; a.n.d, 

 archinephric duct ; g, gonad ; gl, glomerulus ; 

 n, nephrotome ; nc, nephrocoele ; p.c, rudiment 

 of peritoneal canal ; splc, splanchnocoele ; t, 

 tubule ; Z 1 , t 2 , $, primary, secondary, and 

 tertiary tubule rudiments. 



coils and windings as it does so 

 (Fig. 136, E) while the Malpighian 

 body dilates and its dorsal wall 

 becomes invaginated to form the 

 glomerulus. 



As a rule the primitive con- 

 tinuity of nephrotome with the 

 splanchnocoelic lining disappears in 

 the Amphibian as already indi- 

 cated, but it becomes re-established 

 by a peritoneal canal developing 

 secondarily (Fig. 136, D) as an out- 

 growth, arising in Urodeles usually 

 from the neck of the Malpighian 

 body and in Anura from a point 

 farther down the apparent tubule, 

 which grows towards and fuses 

 with a thickening of the coelomic 

 epithelium. Such displacements of 

 the communication between Mal- 

 pighian coelome and splanchnocoele 

 are probably of a similar nature to 

 those mentioned in the case of the 

 pronephros of ITypogeophis (see p. 

 226). 



In those parts of the opistho- 

 nephros which are actively renal in 

 function, i.e. the hinder portion in 

 Urodeles and the greater part of 

 the whole length in Anura, there 

 takes place great increase in bulk, 

 associated with the development 

 of generations of subsequent 

 tubules. Such secondary, tertiary, 

 etc. tubules make their appearance 

 amongst the mesenchyme in the form 

 of cellular strands which resemble 

 closely — both in their original 

 appearance and in the series of 

 changes which they pass through 

 — those from which the primary 

 elements arise (Fig. 136, F, t 3 ). 

 Eventually the secondary tubule 

 comes to open into the primary 

 tubule, the terminal section of which 

 thus forms a collecting -tube com- 

 mon to both, while the tertiary 

 tubule similarly comes to open into 



