SEXUAL ACTIVITY OF MALE RABBITS 581 
at birth, at weaning time or thirty days, and at ninety days. 
The object here sought is to find out if there is a greater varia- 
bility in any one of the service groups, which might be expected 
if any of the service groups contain weak offspring. This study 
will also reveal if heavy service tends to produce a wide range 
of variability in birth weight or a wide range in the weights of 
individuals at the time that they are thrown upon their own re- 
sources at weaning time, and it will show further if the individuals 
tend to deviate more from the mean as they grow older. Devia- 
tions, if they are going to occur, might be expected to occur, 
more strikingly at these three periods than at any other time 
during the observations. This coefficient of variability was de- 
termined by the following formula: 
q 
(Sum of deviations of litters from mean)? x (frequency of class) 
For each Sa Oa 
litter in Number of individuals. x 100 ) 
ates | Mean of respective litters. j 
Number of litters in service group. 
The above formula is used-for the birth weights, the thirty- 
day weights, and the ninety-day weights. 
The measurement data secured were combined into one general 
expression, the ‘mean dimension.’ The advantage of using one 
expression to stand for body measurements les in the fact that 
we have a mathematical expression for the cross section of the 
animal. Graphs expressing cumulatively the percentage increase 
in head length and iliac extremes are found to cross between the 
thirty-fifth and fortieth day of postnatal development; but pre- 
vious to this date and later, up to the time of the conclusion of ° 
the observations at ninety days, the graphs bear a close relation 
to each other, therefore it was deemed correct to combine the 
two measurements to obtain the mean dimension. 
The mean dimension was obtained by the following formula: 
Mean head length + mean iliac extremes. 
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