1 921.] Letters, Extracts, and Notes. 753 



variety must revert, and that such a process is in strict 

 accord with Meuflel^s theorv." 



Tlie word "recessive'^ implies that ''dominant^' is used 

 not in its general, but in its technical jNIendelian sense. We 

 suppose that " mutationist " means here a student of 

 Menders principles of heredity, and such a one might be 

 surprised at the views imputed to liim. 



The appearance of certain characters in the Mendeliau 

 ratio is not a theory, but a law deuionstratt'd by experiment, 

 and the " JMendeliau Law'' simply means that such characters 

 will appear in definite proportions in each generation. 



If we suppose that characters which appeared uiuler 

 domestication are recessive, when the domesticated forms 

 interbreed with the wild stock, even if the recessives are so 

 strictly weeded out by natural selection that they never 

 survive to breed, still a certain number of recessives will 

 infallibly appear whenever two heterozygotes interbreed. 

 This, and not necessarily Colonel Meincrtzhagen's assump- 

 tion, is what is in strict accordance with Mendel's Law. 

 Cases in nature are probably never so sim])le as this hypo- 

 thetical one. For instance, recent work on Lepidoptera 

 suggests that in certain cases the recessives are better able 

 to survive than the dominants. 



From the last paragraph on p. 580, and the second para- 

 graph on p. 532, we are led to believe that Colonel 

 Meinertzhagen considers breeding experiments to be of 

 little use in the study of evolution. Yet on p. 535 he 

 notices with approval Kanimcrer's well-known experiments 

 on Ampiiibia, from which '' it Mould appear that acquired 

 characters are indeed heritable." Modern biologists, while 

 acknowledging the interest and significance of Kauimerer's 

 results, would perhaps hardly commit themselves yet to 

 such a final assertion on the Homeric Question in biology. 



Further, there is every reason to believe that MendeFs 

 Law holds for animals in a natural state. Take, for ex- 

 ample, Lang's experiments on Helix nemoralis described by 

 Darbishire (Journ. of Conchology, 1905). Some remarks 

 by the latter (Introduction to a Biology, 1917, pj). 217-219) 

 on the normal and abnormal in inheritance also answer 



