ZOOLOGY — CASTLE. 239 



ZOOLOGY. 



Castle, W. E., Harvard University, Cambridge, Massachusetts, Grant No. 

 612. Continuation of experimental study of heredity in small mam- 

 mals. (For previous reports see Year Books Nos. 3-8.) $1,000 



The experimental studies of heredity begun in the Harvard Zoological 

 Laboratory ten years ago have made good progress since the last report. 

 For seven of these ten years the experiments have been fostered by the Car- 

 negie Institution of Washington. The more important of the experiments 

 could not have been undertaken without the aid which the Carnegie Institu- 

 tion grant has brought directly or indirectly. 



During the past year each of the lines of investigation described in the 

 last report have been continued and several new ones have been added. 



Our present stock of animals consists of about 400 rabbits, 700 guinea- 

 pigs, 500 mice, 1,000 rats, 400 pigeons, and 8 dogs. 



The experiments have been directed toward the solution of three main 

 problems : 



( 1 ) The nature and possible modifiability of Mendelian unit-characters. 



(2) The nature of blending inheritance. 



(3) The possibility of modifying inheritance by environmental influences. 



Certain color-patterns of rats behave as alternative Mendelian unit-char- 

 acters in heredity. They are in reality, however, quantitative variations in 

 amount of pigmentation and are subject to individual variation, and it is be- 

 lieved also to modification by selection. These in brief are the conclusions 

 which are tentatively held as a result of studying some 10,000 pedigreed rats. 

 The purpose is, however, to double this number before venturing to draw 

 final conclusions in a matter theoretically of much importance and in which 

 current opinions are largely against our view. 



In this laborious investigation the grantee has had the assistance of Dr. 

 John C. Phillips, research fellow in Harvard University. With his assist- 

 ance the ovarian transplantation experiments with guinea-pigs described 

 briefly in the last report have been continued. As yet it has not been possible 

 to duplicate the one successful case then reported. The graft takes in about 

 10 per cent of the transplantations made, but in only one animal, so far, have 

 young been obtained. We propose to continue these experiments on a con- 

 siderable scale to see whether characters different in nature from color-char- 

 acters will behave in the same immutable fashion when residing in germ- 

 cells which have been transplanted to a body of different character. A brief 

 account of this work was published in September 1909 (see Bibliography, 

 p. 48), and a fuller report is in manuscript. 



Dr. Phillips and the grantee are also rearing in captivity several species 

 of Peromyscus, a native field-mouse, the most widely distributed of North 

 American mammals, and are endeavoring to hybridize species from widely 



