432 



ROBERT W. HEGNER 



The structure of the egg, formation of polar bodies, segmenta- 

 tion, and distribution of the nucleolar substance was found to be 

 similar in Oophthora semblidis to these processes in Encyrtus 

 aphidivorus (fig. 14). 



A B C 



Fig. 14 Oophthora (redrawn from Silvestri, '08). A, egg with germinal 

 vesicle (A) and 'nucleolo' (N). B, egg containing many cleavage nuclei. C, 

 formation of primordial germ cells (G) at posterior end of an egg. 



II. THE ORIGIN AND SIGNIFICANCE OF THE KEIMBAHN- 

 DETERMINANTS IN ANIMALS 



In the following pages the writer has attempted to describe 

 briefly the history of the Keimbahn-determinants in animals 

 (except the insects), and to determine the genesis, localization, 

 distribution, and fate of these substances. The literature of 

 this subject is rather large and widely scattered, so it was con- 

 sidered advisable to provide selected figures from original sources 

 wherever they would aid in making the discussion more clear. 

 The data regarding the insects have been set forth in the first 

 paper of this series; they will of course be included in the general 

 considerations in this contribution. 



