August 4, 1922] 



SCIENCE 



145 



course, not so intensively as in America or otlier 

 countries. 



Sorry to confess, I was unable until now to 

 send you our literature including that which was 

 published during the last few years. Perhaps I 

 will have this possibility in the near future. 



Such bits of information fairly well charac- 

 terize the conditions under which Russian men 

 of science are obliged to live and to keep the 

 "light of knowledge burning," in anticipation 

 of better days for .science in Russia. 



M. I. VfOLKOFF 



University of Illinois 



SCIENTIFIC BOOKS 



Genetics, An Introduction to the Study of 

 Heredity. By H. E. Walter. Revised edi- 

 tion, pp. XVI + 354, 9"2 figs. The Maomillan 

 Co., New York. 



This revised edition of a book originally pub- 

 lished in 1913 brings the elemental facts of 

 genetics up to date, and meets at once a need 

 for a popular presentation for the general 

 reader as well as an introduction to the study of 

 heredity for the beginning college student. The 

 enormous progress in this field during the last 

 ten years has necessitated eliminations, addi- 

 tions, and modifications in the former text. 



About 82 pages have been added in the 

 present edition, 50 of which form three new 

 chapters. A new chapter on the "Factor 

 Hypothesis" contains much material that was 

 formerly discussed under "Old Types and 

 New," but the rearrangement of materials 

 places the subject matter in a more logical 

 position and allows a distinct and important 

 concept to be treated as a separate unit. 

 Hereditary genes are here classified roughly as 

 single or plural according to ways in which 

 they determine the visible hereditary character. 

 Of the plural genes, the discussion of genetic 

 modifiers is the most important new subject, 

 since modifiers play such a large part in 

 present explanations for the results of selec- 

 tion. An entirely new chapter on the "Archi- 

 tecture of the Germ Plasm" reflects the most 

 important advances made since the original 

 edition was published, and deals with the con- 

 ceptions and viewpoints based largely on the 

 famous Drosophila experiments, such as link- 

 age, crossing over, the chiasmatype theory, 



interference, and the arrangement of the genes. 

 The author takes the point of view "that it has 

 been possible in a single chromosome to deter- 

 mine not only the relative arrangement of over 

 thirty genes but also to find out the relative 

 distance between these genes." While the order 

 of the genes may be determined readily, our 

 conclusions as to distances between genes have 

 perhaps outstripped the demonstrable evidence. 

 If two linked genes show 1.5 per cent, recom- 

 binations, it still remains to be proved that the 

 low percentage of crossing over is due to or 

 proportional to a short distance between these 

 genes on the chromosome, even in the so-called 

 normal population. Possibly it may be, but 

 there are other alternative explanations. To be 

 sure, the possibility of an accurate localization 

 of hereditary genes in their appropriate 

 chromosomes is attractive and even astonishing. 

 While the hypothesis is alluring, the implica- 

 tions ax'e so grave and important, we must 

 await conclusive proo£ A new chapter on 

 "Somatogenesis" points out the problem of 

 biological differentiation which must take place 

 between the invisible genes in the fertilized 

 egg and the Mendelian characters as end 

 products, for during this process many external 

 and internal factors (including endoerines) 

 come into play and contribute to the formation 

 of the somatic characters as we see and study 

 them in pedigreed cultures. The present chap- 

 ter on "Determination of Sex" introduces much 

 new and important material which was un- 

 available ten years ago, and substitutes for 

 some of the former discussion which now has 

 only a historical significance, such topics as 

 polyembryony, sex-linked inheritance, non- 

 disjunction of the sex chromosomes, secondary 

 sex characters in relation to hormones, sex 

 intergrades and the like. Excellent diagrams 

 make clear at a glance the distinction between 

 the cases where the males are heterogamic 

 (producing two types of spermatazoa) and 

 those eases in which the females are hetero- 

 gamic (producing two types of matured ova). 

 Two radical changes occur in the rearrange- 

 ment of materials in the new edition. A chap- 

 ter discussing "Pure Lines and Selection" for- 

 merly preceded Mendelism but now more appro- 

 priately follows this subject because pure lines 

 and selection can be interpreted best in terms 



