SEXUAL ACTIVITY OF MALE RABBITS 607 
TABLE 6 
Sex ratios in service groups. Males to 100 females 
SERVICE 
Ist 5th 10th 15th 20th 
Number of individuals concerned............. 78 76 117 84 UT 
EGA OMS oo EI EEE. Aho Sd Spa S aeaon 129 | Tel 80 | 53 28 
He 
sperm (Bachhuber, ’16) is weakened by excessive functioning of 
the male reproductive organs. Table 6 presented below shows 
the sex ratio of the offspring in the different service groups. 
Table 6 shows that in the Ist-service group there are 129 
males to every 100 females. After the Ist-service group there is 
a regular decline in the number of males produced, with the ex- 
ception of the 10th-service group. There is apparently some 
underlying cause to bring about the high percentage of females 
to males in all the advanced service groups, and there is a direct 
relation between the amount of service previously performed by 
the male and the proportion of female offspring that he will sire. 
The properties of the spermatozoa are perceptibly modified by 
heavy sexual service of males (Lloyd-Jones and Hays, ’17), there 
being a larger percentage of weak sperm in the advanced service 
sperm. 
Two possibilities exist: either female-producing spermatozoa 
are formed more. largely than male-producing spermatozoa as 
the amount of service of the male increases or the male-producing 
sperm are in themselves weaker than the female-producing 
sperm and consequently fewer of them survive to take part in 
fertilization. On the first point there is no evidence available. 
Concerning the second point, Stockard (13) offers the hypothesis 
that in the case of guinea-pigs the larger female-producing sperm 
are more affected by alcoholization of the male than the smaller 
male-sperm producing. In the case of excessive sexual service, 
however, the large female sperm may be more vigorous because 
of their size or their greater chromatin content and thus out- 
distance the male-producing sperm in the struggle of fertiliza- 
tion, thus giving a higher percentage of female progeny in the 
heavy service groups as compared with the light service groups. 
