THE MESOMERE (INTERMEDIATE CELL MASS) 



225 



onephros. By metamorphosis these groups of cortical cells are inter- 

 spersed with strands of medullary cords. The groups migrate from 

 the dorso-mesial side of the mesonephros to its ventral surface where 

 they are found in the adult, extending almost the full length of the 

 kidney. It now consists of clear-cut areas of medullary tissue associ- 

 ated with circumscribed lobes of cortical tissue. This cortical tissue 

 characteristically contains distinct Stilling cells, never to be found in 

 the medullary tissue. We must conclude, therefore, that since the 



Adrenal cortical anlage at the 10 mm. stage of the frog 

 tadpole, showing the syncytial nature of the mass and the pres- 

 ence of pigment granules, (From Stenger and Charipper: 1946.) 



frog adrenal contains both cortical and medullary material its origin 

 is from both mesoderm and ectoderm. 



The Reproductive System. 



The Gonoducts: The Male. In the male the mesonephric or 

 Wolffian duct acts as both an excretory organ (i.e., ureter) and a re- 

 productive duct (i.e., vas deferens) since all spermatozoa pass from the 

 testis into the uriniferous tubule of the mesonephric kidney by way of 

 the vasa efferentia. These tubules are modified anterior mesonephric 

 tubules which convey spermatozoa into the Malpighian corpuscle by 

 way of a permanent opening into the Bowman's capsule. The sperm 

 then continue to the cloaca by way of the uriniferous tubule and the 



