THE DEVELOPMENT OF FASC1OI.ARI A. 



149 



This intimate connection between the velum and the kidneys 

 recalls the " ans.ne " of BitJiynia tcntaculata, described by Sarasin 

 ('83). In this form the relation between the external kidneys and 

 the velum is still more intimate than in these exceptional cases 

 in Fasdolaria. Indeed the velum of BitJiynia seems to be 

 modified into a functional, excretory apparatus, without having 

 renounced its original duties as an organ of locomotion. 



. \rccssory l-.xtcrnal Kidneys. - - One of the most unexpected 



FIG. 7. Surface view of a portion of a functionally active external kidney, show- 

 ing the thickened cell boundaries, the vacuolated cell contents, the amitotically 

 dividing nuclei, and the nucleoli with their surrounding clear areas. Zeiss A obj. 4 oc. 



facts which I have encountered in my study of Fasdolaria 

 embryos is that in addition to the large excretory organs no 

 small proportion of larvae possesses, sometimes in surprising 

 places, accessory multicellular or unicellular external kidneys. 

 In many cases these are found on the underside of the velum just 

 behind the great kidneys ; here they may become a third as large 

 as the primary organs. In other instances single cells of the 

 postoral or preoral velar row, and even of the head vesicle 

 become modified into secondary unicellular kidneys. In some 



