480 THE ZOOLOGIST. 
opinion seems altogether too pretentious, it may be freely 
admitted that the reasons adduced have much more force against 
it than against the view here maintained, that the flapping 
movement is generally continued for only a part of the flight. 
The frequency of the fin-strokes is made the first poimt of 
attack. Referring to the number of revolutions made by the 
bird’s wing per second, which, according to Marey,* are for the 
Sparrow, 13; Wild Duck, 9; Pigeon, 8; Moor Buzzard, 53; 
Screech Owl, 5; Buzzard, 3; Mébius remarks :—‘‘ If Flying-fish 
make a still larger number of fin-strokes per second, then the fin- 
muscles must be able to contract even more rapidly than the 
pectoral muscles of birds and all other vertebrates.” 
Then follows a comparison of the muscles of certain fishes 
with those of mammals, birds and frogs, in respect to the time 
required to execute a muscular contraction—all with a view to 
showing that the muscles of Haxocwtus are incapable of making 
very rapid contractions. The strength of this argument is im- 
paired by two facts ; 1st, the duration of a muscular contraction 
has never been determined for Mxocetus; and 2nd, the number 
of fin-strokes per second has never been estimated, much less 
experimentally ascertained. 
Furthermore, it does not follow, as Mébius asserts, that if the 
Flying-fish make more than thirteen fin-strokes per second, its 
fin-muscles must be able to contract more rapidly than those of 
birds.. That they would be more rapid than those of some birds 
under some circumstances, can be safely asserted, and nothing 
more. The number of revolutions made by the Sparrow’s wing 
in a second is greatly exceeded in the wing of the Humming- 
bird; and the figure given by Marey does not represent the 
maximum number of strokes of which the Sparrow’s wing is 
capable. A complete ‘‘muscle-curve” consists of a “latent 
period,” a contraction and a relaxation, as every tyro in 
physiology knows, and the last two phases may vary much in 
duration according to circumstances. 
Again, the size of the fin-muscles is said to be incompatible 
with the theory that the fins execute true flight. 
The average weight of the entire bird, as determined by 
Harting for thirteen birds belonging to different orders, is 622° 
times that of the pectoral muscles. In the case of Chiroptera, 
* «Animal Mechanism,’ p. 228, 
