22 BIOLOGY 



Lengthening of gestation period. King ('13), makes the follow- 

 ing statements which apply to lactating Albinos, maintained 

 on a mixed diet. 



The gestation period in lactating albino rats is of normal length if 

 the female is suckling five or less young and is carrying five or less young. 



The gestation period may be prolonged from one to six days if an al- 

 bino female, suckling five or less young, is carrying six or more young. 



The period of gestation is always prolonged when a female is suckling 

 six or more young. In these cases the number of young in the second 

 litter seems to have less influence on the length of the gestation period 

 than has the number of young suckled; but if both litters are very 

 large the gestation period may be extended to 34 days. 



5. Superfecundation and superf elation. Superfecundation oc- 

 curs occasionally in the albino rat and causes an interval of two, 

 three or more days between the birth of different members of 

 the litter (King, '13). 



In support of this statement the following instances are cited: 



1) Litter born October 27, 1911; examined November 10, 

 1911, 12 individuals 11 of these weighed about 14 grams each. 

 The remaining one had very little hair, weighed 7.1 grams and 

 appeared 4-5 days old. 



2) Litter born December 20, 1911; examined January 2, 1912, 

 10 individuals 9 of like size weighed 16-17 grams each. The 

 remaining one small; hair just appearing; weighed 10.8 grams. 



3) Litter born February 26, 1912; examined March 11, 1912, 

 10 individuals 3 had their eyes open and weighed 10.1-10.5 

 grams. The remaining seven were apparently but one or two 

 days old and weighed 4.2 grams on the average. 



In rare instances ovulation takes place in the albino rat dur- 

 ing pregnancy and superfoetation occurs. In two cases of this 

 kind litters have been produced at intervals of about two weeks 

 (King, '13, pp. 388 and 389). 



6. Fecundity and weight at birth. At the beginning of ovula- 

 tion in the albino rat Sobotta and Burckhard ('10) find on the 

 average a total of thirteen ova in both fallopian tubes. The 

 largest litter we have noted in the common Albino contained 

 sixteen. One instance also of sixteen fetuses 18 days old has 

 been observed Stotsenburg (MS '15). 



