340 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



acters and thus representing new types or races. This 

 Mendelian feature of the combining and segregating, recom- 

 bining and resegregating of unchangeable unit characters, has 

 much importance for the practical breeder. It is a condition 

 depending upon the character of the germ cells produced by 

 the mated individuals and of their mated offspring rather 

 than of the somatic or general bodily character. For although 

 after the first cross-mating all of the offspring may be like 

 only one of the parents as regards a certain character, it will 

 be found that by allowing them to produce offspring of their 

 own that their germ cells really represent, in presumably equal 

 numbers, the contrasted characters of both parents. 



The Mendelian order of heredity, although simple and easily 

 understandable in its more apparent aspects, cannot be de- 

 scribed in a few words. For a detailed account of it the student 

 should read some such modern treatment of it as Punnett's 

 "Mendelism, "or Bateson's "Mendel's Principles of Heredity." 



A special phase of the problem of heredity is that of the in- 

 heritance of acquired characters. The congenital characters 

 of an individual, which are the outcome of the constitution 

 of the germ cells that produced it, are undeniably heritable. 

 Besides these characters, however, every individual acquires 

 during its life certain characteristics and variations which are 

 plainly due to the direct modification of the body parts and 

 functions by its lesser or greater use of those parts, or by the 

 direct influence of the abundance or scarcity of food, the rigor 

 or mildness of climate, the amount of sunlight or moisture, 

 etc. If these acquirements on the part of the parents are 

 heritable, and many of them are plainly personal adaptations 

 to the particular environment and circumstances of life in 

 which the individual finds himself, then inheritance by the 

 offspring would be a distinct advantage in leading a similar 

 life. If they could start endowed at birth with all their 

 parents had gained, their own going on with the adapting and 

 modifying process would lead to still further change away from 

 the original type, and thus in comparatively few generations 

 a new type much better adapted to a particular kind of 

 environment would be produced. This conception of personal 



