254 G. CARL HUBER 
from a minimum of 24 days to a maximum of 34 days. The aver- 
age number in a litter is six. In lactating females suckling 
five or less young and carrying five or less young, the period of 
gestation usually does not exceed 23 days and may thus be con- 
sidered as normal. In lactating females suckling five or less 
young, while they are carrying more than five young, the period 
of gestation may be prolonged from one to six days. [n lactating 
females suckling more than five young, the period of gestation 
is always prolonged, and may be prolonged to a maximum of 34 
days. Daniel’s studies on the white mouse lead him to formu- 
late the following law: “The period of gestation in lactating 
mothers varies directly with the young suckled.’’ Such exact 
relation between the number of young suckled and the extent 
of the prolongation of the gestation period was not observed by 
King for the albino rat. 
In the albino rat, ovulation occurs spontaneously and is not 
dependent on copulation, which act, however, may precede or 
follow ovulation. Kirkham and Burr state that ovulation 
usually occurs about 24 hours after parturition and that the 
developing ova can be traced in the ovary through the two 
oestrus cycles preceding their discharge. Long, in his study 
No. 3, by Mark and Long, finds that ovulation must occur in 
the albino rat on an average not less than 18 hours after par- 
turition. Sobotta and Burckhard state that ovulation always 
occurs within 36 hours post partem, though at very variable 
periods, often only a few hours after the completion of parturi- 
tion; again, much later. A second ovulation period apparently 
occurs some 30 days post partem, as would appear from the 
successful pairings conducted by Dr. Stotsenburg. This agrees 
with the observations of Melissinos, who found that pairings were 
more numerous when attempted 29 days after parturition, than 
when attempted 20 to 21 days after parturition, as practiced by 
Sobotta. Semination probably takes place in the ampullar 
portion of the oviduct. Relatively few spermatozoa enter the 
oviducts and Sobotta and Burckhard estimate that the life of 
the spermatozoa in the genital tracts of the albino rat is only 
about 10 hours. 
