86 



T. H. MORGAN AND ELETH CATTELL 



There were five cases of crossing-over (males) in a total of 337 

 males. The cross-overs are all of one kind and result from the 

 combination of W and B. The return crosses would be Red- 

 yellows and these did not appear. The Red-yellows are, in fact, 

 less viable than the White-blacks. 



In the reciprocal cross eight large classes are expected. Only 

 two classes of crossing-over were found. This again indicates a 

 close union between R and B : 



LRB d' by LWY 9 



There were nine cases of crossing-over, all males, in 659 males 

 and 818 females. In this cross since all the Fi sperm, both 

 female and male-producing, carry only recessive sex-linked factors. 



