PREFACE. 



THE aim in producing these Chapters was to make them a 

 contribution to current problems of genetics and evolution. The 

 earlier Chapters deal with some of the more recent contributions to 

 genetics, both in plants and animals, particularly as regards 

 questions relating to mutation. This involved comparisons of the 

 mutation phenomena in (Enothera, Drosophila and various other 

 forms. The importance and significance of parallel mutations has 

 also been emphasized. Owing to circumstances for which the 

 writer is in no way responsible it has been necessary largely to 

 curtail the treatment and to omit almost entirely a discussion of the 

 important cytological results concerning mutation in plants and 

 animals which have been attained since my Mutation Factor in 

 Evolution was published in 1915. 



In Chapters VI and VII are cited from the recent literature 

 numerous cases of mutations in plants and animals, and also a 

 selection from the great number of presumptive mutations described 

 as new varieties or species in the systematic journals. The history 

 and geographic distribution of these is often of the greatest interest 

 from the point of view of their probable origin, and the mutation 

 theory has undoubtedly been of great value in interpreting such 

 variations both in wild and cultivated forms. 



In the last five Chapters more general evolutionary problems 

 have been considered. Some of the corollaries of the mutation 

 theory as regards organic structure, and some of its limitations, 

 have been pointed out. In particular, the contrasts between 

 mutational and organismal characters as regards the structure and 

 distribution of organisms, their relation to recapitulation and such 

 problems as those of adaptation, alternation of generations and 

 inheritance of acquired characters, have been considered in so far 

 as space permitted. The aim has been to show that despite the 

 importance of mutations or germinal changes in evolution, they 

 have definite limitations ; and that large fields of organic phenomena 

 will require the neo-Lamarckian factor for their adequate explanation. 

 This is really applying the point of view of Darwin to the modern 

 advances in our knowledge of variation and of the structure, ontogeny, 

 inheritance, distribution, and relationships of organisms. 



KING'S COLLEGE, R. RUGGLES GATES. 



UNIVERSITY OF LONDON. 



