No. 538] REPRODUCTION IN THE BROWN RAT 631 



present at the time they are born, which throws the 

 blame on the female. In fact, I have no direct evidence 

 against the male. 



The young, when eaten, may be devoured at birth or 

 any time within the next four days. It has been sug- 

 gested—I think with a little basis for the statement— 

 that disturbing the parents causes them to eat their 

 young. W. T. Hornaday, in a letter, and Bostock state 

 that the large carnivora are kept from all disturbing 

 influences at and about the time they are giving birth. 

 In rare cases some species devour their young if dis- 

 turbed, but more frequently the young are deserted. 

 My rats were in a room which was kept locked and free 

 from any disturbing influences except my morning visits. 

 Frequently, females by themselves, which built their 

 nests in closed boxes, have had their young and eaten 

 them between my visits. In such cases these females 

 could not have been disturbed. On the other hand, I 

 have taken the young from the nests, weighed them, and 

 even handled them without the mother injuring them 

 when replaced. 



Another suggestion is that the rats have not had 

 enough flesh diet and, when the young are born, eat 

 them to satisfy their desire for meat. Here again I 

 think there is no truth, provided plenty of grain and 

 vegetables are accessible. My rats have eaten their 

 young when on a meat-grain-vegetable diet, as well as 

 when on a grain-vegetable allowance. 



Dr. Slonaker suggests that the same motive, which 

 leads the rats to eat their dead under natural conditions, 

 might also cause them to eat their helpless young. 

 This is in accord with the rat's habit of killing off its 

 weak. 



One of the reasons for eating the young, I think, might 

 be found in the habit that mammals have of thoroughly 

 li eking their young, and in many cases eating the embry- 

 onic membranes, even among the herbivorous animals. 

 It seems but a little step from the eating of the placenta 

 to the devouring of the young. There may be some 



