144 W. F. K. WELDON. 



Sedgwick has shown that the Wolffian duct and segmental 

 tubules arise continuously by differentiation of the cell mass. 

 In the chick, as in the lizard, the independent origin of duct 

 and tubules in the posterior region is probably a secondary 

 character. 



In conclusion, I wish to express my gratitude to the authori- 

 ties of the Zoological Station at Naples for their kindness to 

 me during my visit, and to Mr. Sedgwick for the advice and 

 assistance which he has given me since my return to 

 Cambridge. 



