4 INTRODUCTION. 



experimental study, but for several years I was unable to do so. 

 Through correspondence with Professor S. I. Bailey, who was at the 

 tune director of the Harvard Astronomical Observatory at Arequipa, 

 Peru, I ascertained that a wild species of cavy occurred in that locality. 

 Professor Bailey kindly captured some of the cavies and attempted 

 repeatedly to forward them to me, but without success. The steam- 

 ship companies refused to accept them for transportation on the ground 

 that they might lead to detention or quarantining of their vessels, 

 since all rodents were suspected of being carriers of bubonic plague. 

 After several years of waiting and fruitless negotiation with every 

 chance traveler to Peru with whom I came in contact, I resolved to 

 go to Peru myself and get the desired specimens. Through a grant 

 made by the Carnegie Institution of Washington I was enabled, in the 

 fall of 1911, to carry this resolution into effect. 



The Carnegie Institution of Washington and the Bussey Institution 

 have together provided means for carrying out the breeding experi- 

 ments described in this paper. I wish to express my gratitude to both 

 institutions and to thank the director and other officers of the Harvard 

 College Observatory for hospitality and generous assistance given me 

 at the Arequipa station. I am indebted also to Professor C. J. Brues 

 for kindly bringing me a stock of guinea-pigs obtained by him near 

 Lima, Peru, in 1912. 



