1881. ] Recent Literature. 797 
Our more immediate purpose in noticing this book, has been to 
call the attention of our zodlogical readers to the chapters on 
animal motion and electricity in animals, on the harmony between 
the organ and the function, involving the acceptance of the devel- 
opment hypothesis, and finally the excellent and suggestive chap- 
ter on the variability of the skeleton. 
After discussing the origin of heat, of mechanical work, and of 
electricity in the animal kingdom, in order to establish clearly that 
these forces are the same as those which are seen in the organic 
world, the author proceeds to study mechanical force, and more 
especially to follow it through all it applications to work of differ- 
ent kinds which it executes in an animal. Marey adopts the old 
comparison between an ordinary machine and the animal, the 
organs of the latter corresponding to the parts of the machine, 
and then he insists on the strict relations existing between the 
form of the organs and the character of their functions ; he farther 
maintains that this correspondence is regulated by the ordinary 
aws of mechanics, “so that when we see the muscular and bony 
Structure of an animal, we may deduce from their form all the 
characters of ‘the functions which they possess.” He notices the 
fact that in the kangaroo, essentially a leaping animal, there is an 
enormous development of the muscles of leaping, the g/s/ez, the 
triceps extensor cruris, and the gastrocnemial muscles. In birds 
the function of flight is exercised under very different conditions 
in different species ; so also the pectoral muscles, which move the 
wings vary greatly in different birds. For example, birds which 
have a large surface of wing, as the eagle, gull, tern, &c., give 
strokes of only a slight extent; that depends on the great resis- 
tance which a wing of so large a surface meets with in the air. 
Those birds, however, which have small wings, as the guillemot 
and the pigeon, move them toa great extent. “If it be admitted 
that the first mentioned birds must make energetic but restricted 
movements, and that the second must move with less energy, but 
with greater amplitude of stroke, the conclusion arrived at must 
necessarily be that the first ought to have large and short pec- 
toral muscles, while in the second, these muscles should be long 
and slender.” This is proved, says Marey, by a simple inspection 
of the sternum in different species; “for this bone measures in 
Some degree the length of the pectoral muscles which are lodged 
In its lateral cavities. Thus birds with long wings have a wide 
ri short sternum ; the others have one which is long and slen- 
e WwW 
” 
r. ae 
€xtent of movement, as in the examples which we have just 
