136 



SEX INHERITANCE 



measurements of the sperm of insects, especially 

 those in which the female- and male-producing 

 sperm differ by a large X-chromosome, and the 

 later results of Goodrich in Ascaris incurva show 

 that the two classes of sperm may differ in size to 

 a considerable degree. (Fig. 36 M). 



^* 



' * 





rH°r'-1^ I'' l"l''l^'l^'N° ^l ''632|263539«6 2926 31 27 II 17 12 9 19 4 | A 7 "2]-l-fg]^l-^l-| pi-, 



100 200 300 400 600 600 70Q 800 900 1000 



Fig;. 36M. — Curve showing dimorphism of sperm of Ascaris incurva. 

 a, outline of nucleus of one class, b, of other class of sperm, c, telophase 

 of differentiating division. (After Goodrich.) 



During the long passage up the oviduct of a 

 mammal, it is possible that the lighter male-produc- 

 ing sperm may travel faster than the female-pro- 

 ducing sperm and therefore attain the upper reaches 

 of the oviduct in larger numbers. More males than 

 females would then be expected, and it is note- 

 worthy that this is the case in several mammals, 

 including man. Correns has obtained evidence that 



