ORIGIN OF THE TETRADS 



[91 



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

 CantJiocamptus and draws the same conclusion. In Cyclops stt'enuiis 

 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 

 Ruckert, and in Cauthocamptns) ; at tlie right by breaking of the V-shaped rods (as in Cyclops 

 sti cnuHs, 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 ^ — 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 



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

 Rath. 



