464 ORREN LLOYD-JONES AND F. A. HAYS 
The amount of seminal discharge; 
The number of sperm! per unit volume of semen; 
The type of motion and the rate of motion of sperm in fresh 
semen ; 
Duration of motion of the sperm; 
The certainty of pregnancy induced by the sperm, and 
The size of litter from various services. ‘ 
References to previous published observations will be made 
under the section on which they most directly bear. 
GENERAL PLAN OF EXPERIMENT 
Rabbits were selected as the experimental animal: They are 
large enough to furnish semen sufficient in quantity on which to 
work, and yet thrive well and reproduce rapidly in close con- 
finement and at slight expense of maintenance. The great 
majority of the observations were made upon three males. In 
general the plan was to have the male accomplish, in as rapid 
succession as possible, a certain number of preliminary ‘services’ 
and then to mate him once to the breeding female from which 
the litter was desired. The ‘end services’ from which litters 
were secured for the progeny studies were the 5th, 10th, 15th 
and 20th, and about an equal number of Ist-service litters were 
obtained as controls. However, when semen studies were made 
it was aimed to recover specimens from the Ist and from every 
5th service thereafter; thus, in a series of 20 services, five speci- 
mens of semen would ideally be recovered for study. This 
ideal set of specimens from a 20-service series was seldom ob- 
tained, however. 
In order to provide females for the ‘preliminary matings’ 
special provisions were necessary. <A single female rabbit will 
sometimes receive the male as many as fifteen times in the space 
of about two hours; but, on the other hand, a female may, 
though she shows every indication of ‘heat,’ refuse the male 
after three or four services, and it is not feasible to commence a 
1 Throughout this work the word sperm will be used instead of the techni- 
cally more correct but cumbersome spermatozoa. 
