ACQUIRED CHARACTERS IN ANIMAL BREEDING 489 



insuperable difficulty to an acceptance of the possibility of any germinal 

 influence by the soma. It is true that Spencer's theory of the unceasing 

 flow of protoplasm through the body, and Darwin's theory of pangenesis 

 by which the body cells were supposed to throw off gemmules which pass 

 to the germ cells were advanced to account for a direct relation between 

 body and soma, but even in more refined form such hypotheses have 

 received not the slightest verification. The present conception of the 

 complex organization of the germinal material, which has been outlined 

 in detail in the first part of this text, adds to the difficulties in the way of a 

 conception of an interrelation between body and stirp. Weismann em- 

 phasizes this difficulty in the statement that the belief that a functional 

 modification may be reflected in the corresponding constituents of the 

 germ-plasm "is very like supposing that an English telegram to China 

 is there received in the Chinese language." This, however, is undoubt- 

 edly an overstatement of the difficulties involved, for the nuclear con- 

 stituents of each and every body cell is on the whole the same as that of 

 the germ cells. Accordingly it is not inconceivable that a bodily effect 

 might be impressed upon the germ cells by hormones liberated into the 

 blood stream by the nuclear constituents of affected body cells. 



The Inadequacy of Affirmative Evidence. All the evidence which 

 has been presented in support of the inheritance of acquired characters 

 fail to satisfy some one or other of the conditions necessary for a rigid 

 proof. Attention has already been called to the fact that the transmis- 

 sion of the effects of mutilation definitely can be denied. For twenty- 

 two generations Weismann cut the tails off mice at birth, yet there was 

 no effect upon the length of the tails of new-born mice. 



The case for environmental effects appears to be in no better con- 

 dition. Here in particular we meet with the kind of evidence which 

 practical men consider favorable to the theory of the inheritance of 

 acquired characters. The hardy little Shetland pony has been bred for 

 centuries on the rocky islands of Shetland where climate is unfavorable 

 and provender often scarce. What more natural than to assume that 

 this scantiness of food has had cumulative, stunting effect from gen- 

 eration to generation until now the average height is only from 40 to 42 

 inches, and many are much smaller? This belief is further strengthened 

 by statements to the effect that under more favorable conditions there 

 is a progressive increase in size. Thus we find in one account of the 

 Shetland pony this statement, "On the prairies of the American corn 

 belt the pony tends to increase in size from generation to generation" 

 The italics are ours, for the fact must be emphasized that an increase in 

 size would not of itself be evidence of inheritance of an acquired 

 character, even though it persisted through any number of generations. 

 An increase in size under more favorable conditions is indeed to be 



