96 HEREDITY [ch. 



those obtained by Tower (Chap. Ill), may have been 

 brought about by the action of environment on the 

 eggs at the time of maturation, but they differ from 

 Tower's in the regularity of their appearance and in 

 being adaptive. Further work in this direction will 

 be awaited with interests 



• Keference must also be made to the work of Sumner [32 a] who 

 finds that rats kept at a high temperature differ in several particulars 

 (proportions of the body, etc.) from those kept in a cold room. These 

 characteristics are inherited to a measurable extent, and the ex- 

 planation offered in the case of insects, that the germ-cells were 

 directly affected by the temperature, is not easy to apply to a warm- 

 blooded animal. There may of course be indirect effects, brought 

 about by a change in general constitution, but the admission of this 

 hardly differs from accepting the inheritance of acquired characters. 

 A considerable list of cases of the transmission of environmental 

 modification, chiefly but not entirely in plants, is given by M^Dougall 

 [22 a]. An important contribution to the subject is the recently 

 published work of Boas, reviewed in Nature, Nov. 3, 1910, p. 11. He 

 finds from a study of the children of European immigrants into New 

 York that whatever the racial characters of the parents, the children 

 born after their arrival in America tend to approach a certain type, 

 and approach it more nearly, the longer the parents have lived in 

 New York. For example, the children of a long-headed race have 

 progressively shorter and rounder heads, the longer the parents have 

 lived in America before their children are born, while those of round- 

 headed parents become longer so as to approach the same type. 

 In this case there is no question of the inheritance of 'acquirements' 

 in the ordinary sense, for the shape of the parents' heads is not 

 affected ; it appears that either the germ-cells or the young childien 

 themselves are affected in such a way as to cause them to approach 

 a characteristic American type in head-shape and other characters. 



