ORIGIN OF THE TETRADS 



191 



Hacker ('92) has reached exactly similar results in the case of 

 CantJiocamptus and draws the same conclusion. In Cyclops strenuns 

 he finds in the case of first-laid eggs a variation of the process which 

 seems to approach the mode of tetrad formation in some of the lower 

 vertebrates',' In such eggs the primary double rods become sharply 



a 



Fig. 95. Diagrams of various modes of tetrad-formation. [HACKER.] 



a. Common starting-point, a double spireme-thread in the germinal vesicle ; d. common re- 

 sult, the typical tetrads; b. c. intermediate stages: at the left the ring-formation (as in Diaptomus, 

 Gryllotalpa, Heterocope) ; middle series, complete splitting of the rods (as in Cyclops according to 

 Riickert, and in Canthocamptus} ; at the right by breaking of the V-shaped rods (as in Cyclops 

 sffcitiius, according to Hacker, and in the salamander, according to vom Rath). 



bent near the middle to form V-shaped loops (Fig. 96, C\ which finally 

 break transversely near the apex to form the tetrad l a process which 

 clearly gives the same result as before. An exactly similar process 

 seems to occur in the salamander as described by Flemming and 



1 Hacker upholds this account ('95, i) in spite of the criticisms of Riickert and vom 

 Rath. 



