290 Scientific Intelligence. 



is necessary for a reaction the products of which are the internal 

 secretions (hormones) of sexual differentiation. Goldschmidt's 

 theory of this antagonistic hormone, or endocrine, action is, 

 briefly, that if the potency of the male differentiating hormone 

 exceeds that of the female activator by a certain amount the indi- 

 vidual develops the sexual characteristics of the male, and vice 

 versa. An approach to equality of hormone potency results in 

 sterile, intersexual (hermaphroditic) individuals. He shows 

 from experimental data that by mating animals selected for a 

 particular sex potency any desired preponderance of either sex 

 or of exclusively intersexual offspring can thus be obtained. 



The book contains an excellent summary of our present knowl- 

 edge of the sex-determining mechanism and its action in the 

 various groups of animals. w. r. c. 



3. Biology, General and Medical; by Joseph McFarland. 

 Fourth edition, thoroughly revised ; 473 pages, with 151 illustra- 

 tions. Philadelphia and London, 1920 (W. B. Saunders Co.). — 

 The wide usefulness of this college text-book, in which the general 

 principles of both plant and animal biology are correlated with 

 such more distinctly human applications as blood-relationship, 

 infection, immunity, parasitism, inheritance, mutilation, regen- 

 eration, grafting and senescence, is shown by the fact that three 

 complete editions have been exhausted in the ten years since the 

 book first appeared. This, fourth, edition has received such 

 revision as was necessary to keep the work in line with recent 

 discoveries. w. r. c. 



4. An Introduction to the Study of Cytology; by L. Don- 

 caster. Pp. xiv, 230, with 24 plates and 31 text-figures. Cam- 

 bridge, 1920 (University Press). — Inasmuch as all biological 

 phenomena are dependent upon the activities of the individual 

 cell, or cells, of which the various organisms are composed, the 

 search for an explanation of any of these phenomena leads 

 directly to the study of the cell. In the past few years the dis- 

 coveries in this field have been so numerous and so important 

 that the subject of Cytology is now recognized as a special science 

 and as one of the most important branches of biology. The phe- 

 nomena of heredity, of development, of sex determination, 

 growth, metabolism, reproduction, disease and death can, in 

 many cases, be associated with certain of the wonderful mechan- 

 isms of the cells. The determination of the sex of an individual, 

 for example, appears to depend upon the presence or absence 

 in the fertilized egg of a particular one of the many chromosomes. 

 In fact, many of the hereditary characteristics in various groups 

 of organisms have been shown to be the result of the actions of 

 genes situated in more or less definitely localized portions of the 

 individual chromosomes. Only from the study of such cell 

 mechanisms do the observed facts of heredity become intelligible. 



The general structure and activities of each of the numerous 

 organs of the cell are described in this book and the function of 

 each of the cell mechanisms are explained as fully as is possible in 



