10 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. In 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. 



