190 Descendenz und Hybriden. 



Castle, W. E., The Mutation Theory oi Organic Evo- 

 lution from the Standpoint of Animal Breeding. 



Points out the necessity of the investigator along these 

 iines becoming a breeder and ilkistrates with certain specific 

 instances from his own experience. In experiments with guinea- 

 pigs established a race oi these animais with four toes, a race 

 not created by selection, ahhough improved by it. Also 

 mentions another, a long haired race, which similarily came 

 into existence. Further discusses the question of the production 

 of new breeds as influenced by crossing. Considers that mu- 

 tations have an internal origin and are relatively independent 

 of environment. Points out the importance of determining 

 wether the extreme fluctuating series frequently found in domes- 

 ticated animais have their origin in mutations. 



CONKLlN, E. G., The Mutation Theory from the Stand- 

 point o f C y t o 1 o g y. 



Discusses the relation of the theory to the ideas regarding 

 the germ cells. Concerning the possible modifications of which, 

 that may lead to mutations in the adult organism, the cytolo- 

 gical investigator is especially interested. As to the nature of these 

 germinal mutations and their relation to the adult conditions 

 the question passes into the realm of mere hypothesis. The 

 main question raised is whether some sudden alteration in the 

 germinal Organization may not be the basis of the origin of 

 new types. 



DwiGHT, T., M u t a t i o n s. 



Discusses the question from the standpoint of anatomical 

 facts as observed chiefly in man. Concludes that it is impos- 

 sible to find support for the idea of evolution as a result of 

 continuous minute changes, but that this line of evidence while 

 not necessarily favorable to the mutation concept, is not in 

 disaccord with it. 



Bailey, L H., Systematic Work and Evolution. 



Discusses the relation of the the mutation theory to the 

 concept of species. Concludes that the new definition of species- 

 concepts must rest on physiological or functional grounds and 

 not merely on a morphological and anatomical basis. Further 

 points out the artificiality of purely taxonomic species. Questions 

 whether two kinds of species shall be recognized ; one of 

 taxonomic, the other of biologic significance. 



Wheeler, W. M., Ethology and the Mutation Theory. 

 Points out that in addition to the physiological and mor- 

 phological characters , the ethological peculiarities must be 

 considered in the investigation of the phenomena of mutation. 

 in applying ethology to this question must seek the discrete 

 idiosyncrasies of behavior between organic species. Considers 

 that an explanation of the origin of instincts may be looked 



