448 University of California Publications in Zoology [Vol. 13 



of life in some mammalian group that the work described herein 

 was undertaken, over two years ago. There was no expectation that 

 any new light could be thrown on the cause of specialization, but it 

 seemed possible that, by carefully studying the nature of specializa- 

 tion in some type, a close correlation might be established between 

 the habits and environment and the modified anatomy of the form. 

 In connection with the carrying out of this study. Professor 

 J. Frank Daniel, of the University of California, has given constant 

 advice and assistance, and has verified the greater part of the 

 anatomical work. Professor C. A, Kofoid suggested the general line 

 of study and the idea of quantitative comparison of structures. 

 Professor J. C. Merriam has given Indispensable advice on several 

 questions of osteology. Many valuable suggestions and a large part 

 of the material for study have been furnished by Dr. Joseph Grin- 

 nell and Mr. F. H. Holden of the California Museum of Vertebrate 

 Zbology. To these persons the sincere thanks of the author are due. 



CORRELATION OF ANATOMY WITH HABITS 



Selection op Material 



The first step in the investigation was to find proper material 

 upon which to study correlation between habits and anatomical 

 structure. Several considerations had to be taken into account in 

 selecting the group of mammals and the individual species to be 

 studied: (1) The mammal for particular study should be highly 

 differentiated from the primitive type; (2) its habits of life should 

 be distinctive; (3) other members of the same group should be 

 numerous; (4) material should be plentiful enough for thorough 

 verification. 



The California pocket gopher, Thomomys hottae (Eydoux et 

 Gervais), seemed to meet all the above requirements to a greater 

 extent than any other form available. The pocket gopher is highly 

 specialized; its habits are characteristic; there are many other 

 rodent families, some of which are more generalized, while some are 

 specialized along different lines; material is in all cases abundant. 

 These facts make the gopher an ideal subject for a study in ana- 

 tomical adaptation to habits of life. 



The pocket gopher differs from the general rodent type in almost 

 every particular, and a detailed study of every organ and system 



