195? ] Ghouri and McFarlane — Reproductive Isolation 33 
whereas the spermathecae of females in the former crosses 
invariably contained sperms. 
Although the ovaries of females in the crosses between 
the strains were apparently normal, containing large 
numbers of eggs, these females laid a smaller number of 
eggs than did the females mated with males of the same 
strain. A female of the Canadian strain generally with- 
held her eggs until the last days of her life. On the other 
hand, Pakistani strain females mated to Canadian strain 
males laid eggs comparatively earlier than the Pakistani 
females mated to Pakistani males. 
Individuals of the two strains are not separable by 
any consistent structural differences (their morphology 
has, however, been far from adequately studied, and it is 
quite possible that obvious differences do exist) ; however, 
the strains may still be distinguished by average dif- 
ferences in appearance and behaviour. The average size 
of the body, ovipositor, the genital openings and sperma- 
tophores of the Canadian strain adults are larger than 
those of the Pakistani strain. The color of the Pakistani 
strain adults varies from light brown with distinct mark- 
ings on the head to very dark brown with scarcely per- 
ceptible markings, whereas the adults of the Canadian 
strain are generally light brown and do not show as much 
variation (both light and dark Pakistani adults were 
used in the crosses). Individuals of the Canadian strain 
are docile and seldom take to wing; on the other hand, 
adults of the Pakistani strain are comparatively active, 
and have been observed to fly as many as 50 yards at a 
stretch. 
In spite of the mating sounds and courtship of the males 
(as described by Khalifa, 1950), neither the Pakistani 
nor the Canadian strain females showed interest in the 
males of the other strain. In the crosses, females of the 
Canadian strain often devoured the smaller males of the 
Pakistani strain. 
Effect of removal of tegmina of males 
The stridulation of the male cricket has commonly been 
considered to be important in attracting the females. 
