ZOOLOGY. 319 



selection, a question which has deservedly received much attention 

 from biologists in the last 15 years. The tendency has been, largely 

 on theoretical grounds, to discredit selection as an agency in evolu- 

 tion, in favor of mutation. Our results indicate that selection is in 

 animal breeding a more important agency than mutation, partly 

 because it is controllable and so its results are more certain, and 

 partly because it may even determine the occurrence of mutations 

 of a particular sort. We have recently presented for publication 

 our full data. 



Dr. Phillips and the writer have also prepared for publication 

 further data on ovarian transplantation in guinea-pigs, which sub- 

 stantiate results previously obtained. In three cases, two of which 

 were mentioned in Year Book No. 10, transplanted ovaries functioned 

 in the production of living young which showed color characters borne 

 by the animal which furnished the ovary but not by the animal which 

 bore the young. These color characters were transmitted to later 

 generations of offspring in the ordinary way and without observable 

 modification. 



Mr. C. C. Little's results from his studies of the inheritance of color 

 in mice, which have been in progress for several years under the 

 writer's direction, has recently appeared in Publication No. 179, 

 illustrated with 5 colored plates. This same pubHcation contains 

 in a separate paper the writer's full data concerning the production 

 through crossing and the fixation as a racial character of the agouti 

 coat-pattern of guinea-pigs, the general results of which were briefly 

 announced several years ago. 



Dr. E. C. MacDowell's studies of size inheritance in rabbits have 

 been submitted for publication. The animals most recently reared 

 in his experiments attained maturity several months ago, since which 

 time his data have been undergoing statistical study and analysis. 

 His results indicate that size inheritance in mammals, although it is 

 correctly described as "blending or intermediate," is capable of expla- 

 nation as a form of Mendelian inheritance involving many indepen- 

 dent factors without the occurrence of dominance. This interpreta- 

 tion, however, presents no practical advantage and may have to be 

 revised later. The important point in Dr. MacDowell's work is the 

 careful determination of the facts, which are fully recorded in his 

 paper. Dr. MacDowell, after two years of service as my assistant, 

 became a year ago instructor in zoology in Dartmouth College, and 

 is now organizing work in animal genetics at Yale University. 



Dr. John Detlefsen, formerly my assistant in charge of certain 

 experiments with guinea-pig hybrids, became a year ago assistant 

 professor of genetics at the University of Illinois. During the past 

 year he has, with the consent of the authorities at that institution, 

 devoted considerable time to the study of material accumulated from 



