414 DEVELOPMENT OF ORGANS IN MAMMALIA. [CHAP. 



is found to he continuous with the sympathetic nervous 

 system. 



On the 16th day processes from the sympathetic 

 mass enter the mesoblastic tissue and become trans- 

 formed into the medullary portion of the adult supra- 

 renal; while the mesoblastic tissue gives rise to the 

 cortical layer. 



The urinogenital organs. 



The history of these organs in Mammalia, excepting 

 so far as concerns the lower parts of the uriaogenital 

 ducts, is the same as in the Chick. 



The Wolffian body and duct first appear, and are 

 followed by the MiiUerian duct and the kidney. The 

 exact method of development of the latter structures 

 has not been followed so completely as in the Chick; 

 and it is not known whether the peculiar structures 

 found at the anterior end of the commencing MiiUerian 

 duct iu Aves occur in. MammaUa. 



The history of the generative glands is essentially 

 the same as in. the Chick. 



Outgrowths from a certain number of Malpighian 

 bodies in the Wolffian body are developed along the 

 base of the testis, and enter into connection with the 

 seminiferous stroma. 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. 

 Similarly intrusions from the Malpighian bodies make 

 their way into the ovary of the female, and give rise to 

 cords of tissue which may persist throughout life. 



The vasa efferentia {coni vasculosi) appear to be 

 derived from the glandular tubes of part of the Wolffian 



