Summarizing, we may arrange characters as follows: 

 A. Congenital Characters 



(a). Inherited (growing under the 

 stimulus of function and envi- 

 ronment. 

 (b) Variations. 



An individual 

 is made up of 



B. Acquired Characters obtained 



(a) by action of environment, 



(b) by function. 



(a) — Inheritance of Acquired Characters or Somatic 



Modifications 



It will be recalled that Lamarck's theory of evolution 

 involved the inheritance of the acquired characters ob- 

 tained through the effects of use and disuse of parts. Dar- 

 win's Theory of Natural Selection also implies the herit- 

 ability of useful variations. But this proposition has been 

 challenged by many recent investigators, the chief being 

 Weismann. E. Davenport (Principles of Breeding) and 

 others assert that the term "acquired characters" should 

 not be used, inasmuch as the modifications referred to are 

 "differences in degree not in kind," and, therefore, are not 

 new characters nor acquired characters. In the discussions 

 on this question, as a rule, zoologists are opposed to the idea 

 of transmission of acquired characters, and many botanists 

 are in favor of it. The two camps have been called the 

 Neo-Darwinian and the Neo-Lamarckian respectively. 



The distinguishing tenets of Neo-Darwinism are: Var- 

 iation is of sexual or internal origin, and acquired charact- 

 ers or somatic modifications are not hereditary. Those of 

 Neo-Lamarckism are: External causes or the environment 

 are directly responsible for much variation, and acquired 

 characters are often hereditary. 



Everyone knows that modifications are acquired by 

 the individual during its life-time, under the influences of 

 the conditions to which it is exposed. Living things must 

 in many cases adjust themselves to the changing conditions 

 of their surroundings. Usually the penalty of non-adjust- 

 ment is death. 



Acquired characters or somatic modifications may be 

 arranged into four groups: 



(1) Mutilations. 



(2) Diseases. 



58 



