224 NATURAL SSCIENCE. Marcu, 
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 differently 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 Mammats. 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. 
Atmost 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 tothe 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 
