SEXUAL ACTIVITY OF MALE RABBITS 465 
series of fifteen or twenty preliminary matings without having 
at least two females in heat in addition to the female which is 
to receive the ‘end service. Moreover, inasmuch as the semen 
specimens were recovered from females after a natural service 
by the male, it was necessary to have an unused female for every 
five services made, or at least for every specimen of semen 
which is to be recovered. In practice a long series of matings 
was never commenced unless at least three and preferably four 
or five females were in heat at the same time. The oestral 
period in rabbits recurs every two weeks if the female does not 
conceive, and the period of gestation is about thirty-one days. 
Females will always receive the male the day following parturi- 
tion, but females in this condition may not be used for recovery 
of semen because of the presence of large amounts of blood and 
other fluids residual from the foetal nutrition. Thus, to carry 
on the work with normal! females, an excessively large stock of 
animals would be necessary. To cut down the number of fe- 
males necessary to provide the preliminary matings a consider- 
able number were operated upon. The Fallopian tubes were 
sectioned and the free ends sutured. This operation absolutely 
prevented conception and for a year or so after the operation 
the sexual behavior of the female was for the most part other- 
wise unchanged, and heat recurred with fair regularity about 
every fifteen days throughout the year. Females treated thus 
proved to be admirably adapted for our use. 
There were some exceptions to the rule in the behavior of the 
operated stock. A certain agouti female, for example, could be 
induced to accept the service of the male at almost any time if 
the male were aggressive. This female apparently went through 
the regular oestrous cycle, at which time she was much more 
ardent toward the male and would accept many more copula- 
tions than at other periods. <A certain sooty female also showed 
a similar tendency. Attempts to secure copulation with other 
operated females when not in heat were unsuccessful. After 
about a year of incessaht copulation many of these operated 
females began to show great pugnacity towards the males, and 
often, though obviously in heat, refused to accept them alto- 
