596 AMNIOTA. 



According to the view of Keinak and Kulliker the outgrowths from tlie 

 ureter give rise to the whole of the tubuli uriniferi and the capsules of 

 the Malpighian bodies, the mesoljlast around them forming blood-vessels, 

 etc. On the other hand some observers (Kupffei", Bornhaupt, Braun) main- 

 tain, in accordance with the account given above, that the outgrowths of 

 the ureter form only the collecting tubes, and that the secreting tuljuli, 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 wliich the tubuli of the metanephros are formed, is derived 

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

 the Wolttiaii 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 out- 

 growths unite with secreting tubuli and Malpighian bodies, formed in situ. 

 1ji Lacertilia the blastema of the kidney extends into a postanal region. 

 Braiin'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 arrange- 

 ment characteristic of Elasmobranchii and Amphibia. 



In the structures connecting the testis with the Wolffian body 

 two parts have to be distinguished, (1) that equivalent to the 

 testicular 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 w^ere first discovered by Braun in Keptilia, 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 seminiferous cells) are subsequently differ- 

 entiated. 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 been 

 detected by myself (No. 555) in Mammals. It is not certain to what 

 parts of the testicular tubuli they give rise, but they probably form 

 at any rate the vasa recta and rete vasculosum. 



In Mammals they also occur in the female, and give rise to cords 

 of tissue in the ovary, which may persist through life. 



The comparison of the tubuli, formed out of these structures, witli 



