380 



THE DEVELOPMENT OF THE CHICK 



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Fig.IM.A. 



Figs. 218 and 219 illustrate the form of these evaginations in 

 duck embryos of 40 and 50 somites respectively, as they appear 

 in reconstructions of the posterior portion of the mesonephros. 



It will be seen that they gradually 

 form sacs opening into the Wolffian 

 duct. Subsequently, by elongating, 

 these sacs form collecting tubules 

 that gather up the secretions of the 

 mesonephric tubules proper and con- 

 duct them to the Wolffian duct. 

 These conducting tubules are stated 

 to branch more or less; it is also 

 said that they are more highly de- 

 veloped in the duck than in the chick. 

 Felix proposes to call them meso- 

 nephric ureters. 



In the case of the secondarv and 

 tertiary tubules, three parts may be 

 distinguished : parts one and two (de- 

 rived from the nephrogenous tissue) 

 are the renal corpuscle and secreting 

 tubule respectively; the third part is 

 the collecting tubule derived by 

 evagination from the Wolffian duct. 

 In the case of the primary tubules, 

 a conducting part appears to be 

 formed secondarily, though in what 

 w^ay is not clear. 



The formation of new tubules 

 ceases on the fifth day, all the ne- 

 phrogenous tissue being then used 

 up. Up to the eighth clay at least 

 the tubules grow rapidly in length 

 and become more differentiated. The 

 result is a relatively enormous pro- 

 trusion into the body-cavity on each 

 side of the dorsal mesentery. De- 

 generation of the tubules sets in 

 about the tenth or eleventh days, 

 and the tissue is gradually absorbed; 



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