560 P. W. WHITING 



The 'change of partners' observed in tetrad stages may have 

 no significance for heredity in the sex in which linkage is com- 

 plete, but may be associated with more important conditions, 

 such, possibly, as breaks and re-fusions in the female of Dro- 

 sophila, the male of Bombyx, both sexes of the rat, and in the 

 development both of pollen nuclei and of ova in Primula and 

 Lathyrus. 



Culex may be expected to give no crossing over of factors in 

 the male, if we may generalize so widely from conditions in 

 Drosophila, but Culex is a fly of relatively lower order taxo- 

 nomically and somewhat nearer to the common stem of Diptera 

 and Lepidoptera. We may perhaps expect to find some con- 

 necting link between Drosophila, in which linkage is complete 

 in the male only, and Bombyx in which linkage is complete in 

 the female only. 



The cytological results in Culex thus far throw no light upon 

 these questions. 



