576 FRANK A. HAYS 
very large amount of labor. Such extensive records were im- 
possible for reasons that need not be discussed here. Weights 
were secured on a sensitive torsion balance and variations of 0.5 
gram were recorded. Great errors may be introduced by a 
‘fill’ if the records are not made at the proper times; therefore 
the records were secured at about the same hour each day before 
feeding, which was done once daily. However, there are cer- 
tain errors in weight records which cannot be avoided by the ex- 
perimenter. The general degree of health of the animals has 
much to do with fluctuations in weight as MacDowell (14) 
found in growth studies of rabbits; nevertheless, as with other 
animals, weight seems to be the best available index of growth. 
Two methods for studying the growth of the progeny produced 
were chosen, namely, growth in body weight and growth in body 
measurements. The first will be discussed here. 
Body weight, according to Minot (’08, p. 87), represents the 
total mass of the living body, while body measurements are only 
partial indices of growth. That individuals show wide fluctua- 
tions in weight Has been pointed out by MacDowell (14, p. 191) 
in his studies on the rabbit. Although growing rabbits show 
marked variability in weight on different days, it was thought 
possible by the use of large numbers to secure growth curves 
that would fairly represent a race of rabbits kept under uniform 
conditions. There is a possibility that these growth curves 
would diverge more as the animals grow older, because Mac- 
Dowell has shown that though most rabbits apparently make a 
a. normal growth to maturity, others fall much below the normal 
and do not reach the average weight in what is considered the 
normal period. But complete records were out of the question 
as indicated above. Even though this is the case, it is very 1m- 
portant to ascertain if this reputed inferiority of progeny which 
is supposed to result from the weaker sperm cells of the over- 
worked male is going to be apparent when his progeny are in the 
most active stage of growth, i.e., during the first ninety days of 
postnatal life. If progeny from the advanced services of males 
are more poorly equipped with the necessary something to en- 
able them to make normal growth, would this not be apparent 
