ZOOLOGY — CASTLE. 243 



ZOOLOGY. 



Castle, W» E*, and Mark, E. L*, Harvard University, Cambridge, Massachu- 

 setts. Grant No. 331. Experwie?ital studies iyi heredity. (For pre- 

 vious reports see Year Book No. 3, p. 136, and Year Book No. 4, p. 

 276.) $500. 



Drs. Castle and Mark are associates of the Department of Experimental 

 Evolution at Cold Spring Harbor, and their work has been done in cooper- 

 ation with that of the Department. 



Abstracts of Reports. — Dr. Castle reports that observations have been made 

 upon about 2,000 guinea-pigs, 1,000 rabbits, and 1,500 rats reared from 

 pedigreed stock. The general questions concerned are, (i) what sorts of 

 variations are concerned in the processes of evolution, and (2) what are the 

 laws governing their transmission ? As in previous years, much attention 

 has been given to color-inheritance, being concerned this year chiefly with 

 color-patterns, particularly with their modification by selection. Other 

 characters studied are polydactylism, skeletal dimensions, general size, and 

 ear-characters. The contrasted ' ' mutation ' ' and ' ' selection ' ' theories as 

 to the origin of new organic forms have been kept constantly in mind, and 

 it is concluded that both are important in evolution. Ivatent inheritance 

 and reversion have received considerable attention, and a most interesting 

 experiment has been an attempt to fix a reversionary heterozygous charac- 

 ter, the agouti coat of guinea-pigs, identical in its general features with the 

 coat-color of wild cavies. 



The results of some selection experiments extending over several years are 

 ready for publication, and others are in preparation. Anatomical studies 

 have been made of hybrids between the guinea-pig and Cavia aperea of Bra- 

 zil. The hybrids are of remarkable size and vigor, but completely sterile. 

 A second importation of Cavia aperea from a different part of Brazil was 

 unfortunately lost in the long ocean voyage to this country. 



Student assistants in the work and the topics upon which they have been 

 engaged are indicated in the following list : 



(i) Mr. P. C. Ackerman. The anatomy of the four-toed foot in the polydactylous race 

 of guinea-pigs ; is it atavistic or not ? Probably atavistic. 



(2) Mr. H. R. Fulton. Can giant and dwarf races of guinea-pigs be established by selec- 

 tion ; if so, are they stable races ? This investigation is still in progress. 



{3) H. MacCurdy. Can color-patterns among spotted guinea-pigs and rats be fixed by 

 selection ? They can not ; but selection can fix within certain limits as racial 

 characters particular amounts of pigmentation ; that is, spotted races can be created 

 at will which bear either much pigment and little white fur or the reverse, much 

 white and little pigment. One can not at will fix the position of the pigmentation, 

 either on the anterior or on the posterior part of the body, or in any other arbi- 

 trarily selected position. This investigation is completed and ready for publication. 



(4) R. C. MuUenix. The inheritance of skeletal dimensions among rabbits. 



