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. 36M). 
60 
40: 
20 
ro cia | 4/12] 12/31] 21 /a8]41 |s}azi2ai aifa7|ufizfi2!9 fro} a}a | 7 | 2}r-f2 prio pry 
100 200 300 400 600 600 700 800 900 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 
