EXCRETORY ORGANS. 723 



accordance with the account given above, that the outgrowths of the ureter 

 form only the collecting tubes, and that the secreting tubuli, etc. are formed 

 in situ in the adjacent mesoblast. 



Braun (No. 542) has arrived at the conclusion that in the Lacertilia the 

 tissue, out of which the tubuli of the metanephros are formed, is derived 

 from irregular solid ingrowths of the peritoneal epithelium, in a region 

 behind the Wolffian body, but in a position corresponding to that in which 

 the segmental tubes take their origin. These ingrowths, after separating 

 from the peritoneal epithelium, unite together to form a cord into which the 

 ureter sends the lateral outgrowths already described. These outgrowths 

 unite with secreting tubuli and Malpighian bodies, formed in sitit. In 

 Lacertilia the blastema of the kidney extends into a postanal region. 

 Braun's account of the origin of the metanephric blastema does not appear 

 to me to be satisfactorily demonstrated. 



The ureter does not long remain attached to the Wolffian 

 duct, but its opening is gradually carried back, till (in the Chick 

 between the 6th and 8th day) it opens independently into the 

 cloaca. 



Of the further changes in the excretory system the most im- 

 portant is the atrophy of the greater part of the Wolffian body, 

 and the conversion of the Wolffian duct in the male sex into the 

 vas deferens, as in Amphibia and the Elasmobranchii. 



The mode of connection of the testis with the Wolffian duct 

 is very remarkable, but may be derived from the primitive 

 arrangement characteristic of Elasmobranchii and Amphibia. 



In the structures connecting the testis with the Wolffian body 

 two parts have to be distinguished, (i) that equivalent to the 

 tcsticular network of the lower types, (2) that derived from the 

 segmental tubes. The former is probably to be found in peculiar 

 outgrowths from the Malpighian bodies at the base of the testes. 



These were first discovered by Braun in Reptilia, and consist 

 in this group of a series of outgrowths from the primary (?) 

 Malpighian bodies along the base of the testis : they unite to 

 form an interrupted cord in the substance of the testis, from 

 which the testicular tubuli (with the exception of the semi- 

 niferous cells) are subsequently differentiated. These outgrowths, 

 with the exception of the first two or three, become detached 

 from the Malpighian bodies. Outgrowths similar to those in 

 the male are found in the female, but subsequently atrophy. 



Outgrowths homologous with those found by Braun have 



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