224 NATURAL SCIENCE. March. 



professor whose lectures he attends. However, if he must buy a text- 

 book, then let him consider two standards by which, in our opinion, 

 a book of this kind should be judged. A book intended for elemen- 

 tary students ought to be of moderate bulk, and it should be 

 thoroughly up to date. In these days of examination, the very 

 newest discoveries are apt to be inquired about by examiners. The 

 book should be rendered fairly portable through judicious condensation, 

 not so pronounced, however, as to produce obscurity. The writer of 

 a text-book should remember that human flesh is weak, and also that 

 time is short. M. Perrier's book is not, judged by these standards, 

 altogether ideal ; still, we gladly admit that it has its good points. 

 Possibly, too, the French student is diflferently placed with regard to 

 examinations. The author might, however, if he had taken thought, 

 have refrained from adding an inch or two to the stature of the book ; 

 this would have been a distinct gain, for we have seldom handled so 

 awkwardly shaped a volume. If there is a second edition it is to be 

 hoped that a fission into two equally-sized halves will take place. 



A feature of M. Perrier's book is the introduction of coloured 

 plates, illustrating, of course, the circulatory system of various animals. 

 The illustrations are not generally very first-rate, and the same 

 remarks apply to the woodcuts and "process" blocks by which the 

 text is really very lavishly illustrated. What is wanting in quality 

 is certainly made up in quantity. Furthermore, the author pays 

 more attention to papers published outside France than is sometimes 

 the case with his countrymen. Altogether, we are favourably 

 impressed with M. Perrier's book. 



Text-Book of the Embryology of Man and Mammals. By Dr. Oscar 

 Hertwig. Translated from the third German edition by Edward L. Mark, 

 Ph.D., Hersey Professor of Anatomy in Harvard University. Pp. 670, with 

 339 figures in the text and 2 lithographic plates. London : Swan Sonnen- 

 schein & Co., 1892. 



Almost as much as in the case of Balfour's great treatise on com- 

 parative embryology, this book is the result of the author's original 

 investigation. The two books have very different purposes. Balfour 

 was practically inventing a new science, and he endeavoured, so 

 far as could be done, to go over the whole animal kingdom, and set 

 forth, in orderly and systematic exposition, the facts and the principles 

 of Comparative Embryology. The very result of the enormous 

 stimulus to research given by his treatise is, that the treatise is now 

 so largely behind our knowledge that it is rather a landmark in 

 history than a text-book for beginners. Dr. Oscar Hertwig has 

 written his book specially from the point of view of the needs of those 

 studying human anatomy. The facts and principles of comparative 

 embryology are used chiefly as a guide to the ontogeny of higher 

 forms. But the student of medicine or morphology who masters 

 this volume will have a large knowledge of comparative embryology, 

 and will have the unity of the animal kingdom strongly impressed on 

 him. It would be difficult to think of anyone from whom a book of 

 this kind would be more valuable, for a large part of the extension 

 of our knowledge has been due to the studies of Oscar Hertwig and 

 his brother on the Cell and the Coelom-Theory. 



Those who have been unable to follow recent developments of 

 embryology closely, will be most interested by the chapters on the 

 middle layer. Not long ago it was assumed that the mesoblast was a 



