32 THE PRINCIPLES OF HEREDITY 



tion and the tissue by which the lost part is replaced (i. e. the 

 scar) as a single acquired character. But surely the mutila- 

 tion ought not to be so designated. It should rather receive 

 some such distinctive name as an enforced character. We see 

 also that the power of regenerating lost parts to a greater or 

 lesser extent persists throughout organic nature, but that 

 this power is vastly greater in low than in higher animals. 

 In other words, if we agree to regard such regenerations as 

 acquirements, observation proves that the power of acquiring 

 them is very much greater lower in the scale (e. g. sponge) 

 than it is higher (e.g. man). The power in fact undergoes 

 diminution (regression) as it grows of less and less import- 

 ance in the struggle for survival, and other faculties take 

 its place. The term " acquired " is now, however, so well 

 established in reference to mutilations, that it is hopeless 

 to expect a change to a more accurate and scientific nomen- 

 clature. Unfortunately just as a lack of clarity in thought 

 frequently results in a lack of clarity in terms, so a lack of 

 definiteness in terms frequently leads to a lack of accuracy 

 in thought. 



54. On the other hand, there is another class of acquired 

 characters perhaps the only class to which the term should 

 be applied the power of acquiring which is greatest among 

 the highest animals, and, apparently, is little or not at all 

 present among the lower animals nor in the plant world. 

 These are such characters as arise as a result of exercise and 

 use, and which from their nature we may term, adaptive 

 acquirements; for instance, the increased muscular power of an 

 athlete. In the plant world such characters cannot be ac- 

 quired to any extent, for vegetables do not " use " their parts 

 in the sense that animals do. Plants, therefore, of necessity, 

 attain their full development in the absence of almost all 

 stimulation other than that supplied by sufficient food, light, 

 and warmth. 1 Of such plant-like animals as sponges the 

 same is true. It is true to some extent, and with many ex- 

 ceptions, even of such active animals as insects. Thus a pupa 

 may develop into a perfect insect while lying quiescent. The 

 lower vertebrates, such as fish and reptiles, also have little 

 power of developing in response to the stimulation of exercise 



1 No doubt, to a limited extent some use-acquirements are made by 

 plants. Thus the Kauri pines of New Zealand, when taken from 

 exposed hillsides, yield timber much tougher and more durable, and 

 therefore more valuable though less easily sawn, than timber taken 

 from sheltered valleys. The ingenious timber merchant endeavours 

 on occasion to sell his valley planks as the product of the hillside. 

 Climbing plants also " use " their tendrils. 



