466 



SCIENCE 



[N. S. Vol. XLIV. No. 1135 



ings, LVIII., No. 347, page viii, Forsyth says : 

 I have heard Cayley describe how Sylvester and 

 he walked round the courts of Lincoln's Inn dis- 

 cussing the theory of invariants and covariants. 



Sylvester told me that the only time he ever 

 saw the placid Cayley beside himself was when 

 in the midst of a discussion on the theory of 

 forms a fat bundle of legal papers was 

 brought in to him. Cayley dashed the plethoric 

 bundle on the floor in an access of chagrin. 



Thus London was the birthplace of this 

 unique friendship, not the Cambridge which, 

 before ever the gentle Cayley came, had sent 

 out Sylvester without even a degree. 



George Bruce Halsted 



Greeley, Colo. 



SCIENTIFIC BOOKS 



A Laboratory and Text-booh of Embryology. 

 By Charles W. Prentiss, A.M., Ph.D., Pro- 

 fessor of Microscopic Anatomy in the North- 

 western University Medical School, Chi- 

 cago. Octavo of 400 pages with 368 illus- 

 trations, many of them in colors. Philadel- 

 phia and London, W. B. Saunders Company. 

 In this new manual of embryology an effort 

 has been made, as stated in the preface, " to 

 combine brief descriptions of the vertebrate 

 embryos which are studied in the laboratory 

 with an account of human embryology adapted 

 especially to the medical student." 



The subject-matter of the book, following an 

 introduction, is divided into twelve chapters. 

 The introduction presents the scope of human 

 embryology, emphasizes its importance to the 

 medical student and includes a resume of the 

 history of the science and a brief statement of 

 the principles of growth and differentiation of 

 the embryo. After a discussion of the meth- 

 ods of study, in which the dissection of em- 

 bryos as a class-room practise is strongly 

 recommended, this section of the book is con- 

 cluded by a short list of carefully selected 

 titles of journals and other works of reference 

 dealing with embryology. Chapter I. is de- 

 voted mainly to a review of those fundamental 

 facts which are usually learned by the student 

 in connection with the biological studies of his 

 premedical preparation. The description ' of 



the human ovum, which is too brief, and the 

 good account of the morphology and develop- 

 mental cycle of the human spermatozoon 

 should have formed part of one of tlje later 

 chapters dealing specially with the human 

 embryo. The reviews of the subjects of cell 

 division, maturation, fertilization and the 

 questions concerning heredity, sex determina- 

 tion and twinning may be amplified, if the 

 student so desires, by consulting a number of 

 original sources and well-known books, to 

 which he is referred by citations in the text. 

 In Chapter II. the topics of segmentation and 

 the origin of the germ layers are treated from 

 a comparative embryological standpoint, am- 

 phioxus, lizard, chick, bat and rabbit serving 

 as representative types. The study of chick 

 embryos is the subject of the third chapter. 

 Here the text and figures are adapted to work 

 in the laboratory. Directions are given for 

 the preparation of specimens for study; de- 

 scriptions of whole embryos and sections in 

 three stages of development are presented. 

 Descriptive embryology is resumed in Chapter 

 TV., which discusses the subjects " fetal mem- 

 branes and early human embryos." Here 

 again the comparative method of exposition is 

 employed with good effect. The main feature 

 of Chapter V., which deals with the structure 

 of small embryos of pig, is the full and careful 

 description of the anatomy of the 10-12 mm. 

 embryo as revealed by study of the surface 

 form, dissections and sections. As this part 

 is adapted primarily for use in the labora- 

 tory, the explanation given in the next chap- 

 ter of the technical methods involved in the 

 preparation of specimens, might better have 

 been included in the present one. The tech- 

 nique of the dissection of embryos evolved in 

 the Harvard Medical School for class practise 

 is described in detail. In the same chapter 

 (VI.) this method is advocated in the study 

 of the face, palate, tongue, salivary glands 

 and teeth. The remaining five chapters 

 (VII.-Xn.), comprising more than half of 

 the book, are an account of the development 

 of the organs and organic systems which the 

 student may consult in connection with the 

 more strictly laboratory work represented by 



