SEXUAL ACTIVITY OF MALE RABBITS Had 
when the young rabbits are thrown upon their own resources, 
as was done during the sixty days following weaning time that 
the records were kept? 
Concerning the second method of studying growth, namely, 
by body measurements, it is important to discover whether body 
development follows apace with body weight and to check one 
against the other. For this reason, all litters born up to August 
9, 1916 (45 in number), were measured as well as weighed, at five- 
day intervals up to the age of ninety days. 
A measure of head length was considered valuable, as measure- 
ments of the skull have been found to be less variable than meas- 
urements of long bones. MacDowell (14, p. 38) found this to 
be true in rabbits. Hatai (’08) observed the same thing in the 
albino rat, and Quetelet (’71) likewise found the same in man. 
The head length as here reported was measured by the use of 
calipers and represents the distance obtained by placing the sta- 
tionary arm at the crest of the occipital bone allowing the beam 
of the calipers to extend sagitally downward parallel with the face. 
The movable arm was then brought up until it rested snugly 
against the end of the nose and down over themouth. The lower 
arm of the instrument was then just beneath the inferior extremity 
of the premaxiliae and the upper arm was just above the superior 
region of the occipital bone. There is very little flesh or soft 
tissue covering the bones in this region, about the only structures 
obscuring the bones are the skin and the hair coat. It is ap- 
parent, that a head measurement in this particular region 
approximates rather closely the actual skull size. 
Since there is the possibility that some other body measure- 
ment would make an entirely different growth curve from that 
of the above-described head measurement, it was considered de- 
sirable to secure one other measurement that could be taken with 
considerable accuracy on the live animals. Moreover, we wished 
to obtain a ‘mean dimension’ from the average of two measure- 
ments, therefore some easy body measurement was searched for. 
There is no little difficulty in securing external méasurements of 
the body with accuracy, as the writer has learned from much ex- 
perience with cattle and swine. A measure of the breadth be- 
