192 EVOLUTION AND ANIMAL LIFE 



in many other cases recorded by post-Mendelian observers and 

 experimenters. These records are of both plants and animals, 

 and are fast multiplying. 



Thus the so-called Mendelian laws of heredity refer to two 

 phases of the problem of inheritance viz.: (1) how inherited 

 characters are actually distributed, and (2) the fundamental 

 cause, lying in the germ plasm, for this particular kind of dis- 

 tribution. Like Galton's formula, Mendel's law expresses the 

 regularity of heredity based on actual recorded statistics of 

 inheritance ; but it also gives a satisfying fundamental reason for 

 this regularity. Biologists, with few exceptions, see in the 

 establishment of the Mendelian principles of heredity in biologic 

 science the greatest advance toward a rational explanation of 

 inheritance that has been made since the beginning of the 

 scientific study of the problem. 



The extraordinary fact that Mendel's work lay practically 

 unnoted for thirty-five years (actually the only reference to it in 

 'scientific "literature " in all that time seems to have been one by 

 Focke in 1881 in Die Pflanzenmischlinge, p. 109), has been 

 partly explained by Bateson as due to the driving interest felt 

 through all that time by biologists generally in other phases of 

 investigation; but it remains a curious commentary on the 

 possibilities of the temporary obscurity that may be in store for 

 even the best scientific work. The "discovery" of Mendel's 

 work seems to have been made in 1900 by three investigators 

 almost simultaneously, who also discovered independently the 

 same important facts of the transmission behavior in inheritance 

 of exclusive or alternative characteristics. These men are de 

 Vries, Tschermak, and Correns, and their published papers not 

 only verify Mendel's particular work on the peas, but confirm 

 his principles or laws on the basis of much added experimenta- 

 tion and observation on other plants. In the last five years 

 zoologists, notably von Gnaita working with mice, Cuenot, 

 Darbishire, Davenport, Bateson and Castle with mice, rabbits, 

 guinea-pigs and chickens, McCracken with certain beetles, and 

 Toyama, Mrs. Bell and Kellogg with silkworms, have shown 

 that Mendelian principles obtain in animal as well as in plant 

 inheritance. For the results of all of these investigations in 

 large measure confirm our confidence in the Mendelian prin- 

 ciples of dominance and recessivity and of the purity of germ 

 cells. But also in nearly all of these studies the investigators 



