60 
known. Those of the frog’s blood being taken as a standard 
of comparison, and observed under the microscope side by 
side, those of birds are about one-half the size of those of a 
frog; those of the salamander not quite one-third larger than 
those of the frog, and rather more elongated ; those of the 
lizard about two-thirds the size; while those of the human 
blood measure only one-fourth the long diameter of the frog’s, 
and only one-twelfth the long diameter of those of the siren. 
The red corpuscles of the musk-deer are exceedingly small, 
being only about one-twentieth the size of those of the frog. 
3. We have the highest medical authority for saying that, 
if the blood introduced into the veins of a living animal differs 
merely in size of its corpuscles, a disturbance, more or less 
remarkable, takes place ; the pulse is increased in frequency, 
the temperature falls rapidly, and death generally happens 
after the lapse of a few days. The effects produced by the 
injection of blood having circular globules into the veins of an 
animal, the corpuscles of whose blood are elliptical, or vice 
versd, are still more remarkable: death then usually takes 
place amidst nervous symptoms of extreme violence, and com- 
parable, in their rapidity, to those that follow the introduction 
of the most energetic poison.* 
Here then, again, judged by its own canon, the whole 
fabric of Hvolution by natural selection falls to the ground. 
4, Another subject worthy of consideration is the adapta- 
tion of the general structure of fish to the element in which 
they live. ‘he resistance which water offers to the passage of a 
body passing through it is very great. When compared with 
air it is as 80 to 1, and yet a fish can pass through it with 
the greatest ease, and this for several reasons. First on 
account of the form and disposition of the vertebral column. 
The backbone of a fish consists of a number of small vertebra, 
having at both ends a cup filled with a gelatinous substance, 
that which is within each pair of cups, thus forming a ball. 
Thus there is a flexible axis with all the appendages somewhat 
flattened. 
Second. The entire body tapers at both ends, so as to 
present to the water no actual line of resistance. 
Third. Most fish possess a particular organ called the swim 
bladder. This organ, which is long and cylindrical, and 
placed along the under side of the central axis, is filled with 
a gas which is many times lighter than water, and thus the 
creature is rendered specifically lighter than it otherwise 
would be. 
* Milne Edwards. 
