BOOK REVIEWS 141 



olution upon such questions as the mechanistic conception of 

 personality, the freedom of the will, and similar problems. The 

 bibliography will be particularly appreciated by those who wish 

 to follow further the topics discussed. 



The Mechanism of Mendelian Heredity is a report of the very 

 excellent work in experimental heredity that has been going on 

 under the direction of T. H. Morgan, of Columbia, for many years. 

 Morgan has found that a little fruit-fly lends itself very well 

 to the experimental study of the phenomena of inheritance. 

 In working with this fly, he has found that in many cases, the 

 Mendelian ratios anticipated do not maintain. He attemps to 

 explain the apparent exceptions on the conception that the de- 

 terminers are not permanently fixed in particular . chromosomes 

 but may move from one chromosome to another as parts of dif- 

 ferent chromosomes interchange during the cell divisions. The 

 book explains this theory of linkage and crossing over, devotes a 

 chapter to sex inheritance, and then discusses in the latter part 

 of the book similar phenomena in other material, both plant and 

 animal . 



There is an extensive bibliography of 20 pages, which will be 

 welcomed by the specialists in this field. The book is not a pop- 

 ular presentation, but is intended for students. However, it is 

 so well written and illustrated that a lay reader will be able to 

 follow T the matters disaissed, with careful attention and some 

 study. No better work than this is available on the present 

 status of our knowledge in regard to inheritance. 



