262 Notices of Books. (April, 
of a young student side by side, as joint author, with that of 
the able Prelector in Physiology. A few years ago physiological 
laboratories were almost unknown in this country: the work 
before us promises a splendid proof of what may be done in 
them, and of the value of the results to be obtained by a term 
or two of patient work. This book is only the first part of a 
systematic introduction to the whole subject of Embryology, and 
since the chick is not only ‘‘ of all embryos the best to begin 
with,” and also the most easy to obtain, and in many respects 
to manipulate, the Authors have taken it, from the new-laid egg 
to the chicken, as their starting-point. And they express hope, 
at the commencement, that the student will not content himself 
with merely reading the book, but that he will dissect for him- 
self, in which he will be aided by many practical instructions, 
and by some beautiful and original drawings. The work is 
divided into nine chapters, which treat of the structure of a 
hen’s egg, of incubation, of the changes which take place during 
respectively the first, second, third, fourth, fifth, sixth, and so 
on to the end of incubation; a final chapter on the development 
of the skull; and an Appendix, containing practical instructions 
for studying these various changes. Of the woodcuts we may 
specially mention Fig. 1, which shows a section of an unincu- 
bated fowl’s egg; Fig. 13, showing the circulation of the yolk- 
sac at the end of the third day of incubation; and Fig. 71, 
showing the embryonic skull of a fowl during the second week of 
incubation. The formation of each particular organ—eye, ear, 
heart, &c.—is traced and illustrated in a most masterly manner. 
The book will be a great addition to our study of physiology. 
Although not suitable for school use, we have no doubt that the 
work will soon be adopted wherever examinations in physiology 
are held, and by those colleges which require physiology as one 
of the subjects of their Science scholarship examinations. 
An Elementary Exposition of the Doctrine of Energy. By D. D. 
Hearn, M.A., formerly Fellow of Trinity College, Cam- 
bridge. London: Longmans, Green, and Co. 1874. 
Tuts is a capital and comprehensive little book. It embodies a 
series of lectures given in 1872 to the sixth form of the Surrey 
County School. Mr. Balfour Stewart has an “ Energy Class” 
at Owens College, and in process of time we shall have this 
great and dominant doctrine taught in all our larger schools. The 
sooner that time arrives the better, for we have already a good 
text-book in the work before us. It might, however, with advantage 
be somewhat subdivided, and the addition of a table of contents 
and of an index would enhance its value for purposes of reference. 
The Author gives at the outset a series of typical changes :-— 
1. A head of water confined by a sluice gate. 2. The sluice 
