VITAL PRINCIPLE. 25 
be controlled by the same laws which regulate the offspring 
of univocal generation, as to form, structure and duration ; 
and that the same beings should be able to continue, by 
transmission, that life which they derived from accident ? 
The most rational explanation which can be given of the 
appearances of these plants and animals, in such places, is 
derived from the consideration of the smallness of their 
seeds or eggs, which may be carried about by the winds, 
and showered down along with the rains, so as to enter 
with facility into every situation. They cannot, how- 
ever, expand, unless in circumstances favourable to 
ther future growth. Thus the soil, in which alone the 
beautiful little plant called Monilia glauca makes its ap- 
pearance, is the surface of putrid fruit; while the small 
animal termed Vibrio aceti, requires for its growth, vinegar, 
which has been exposed for some time to the air. This 
view of the matter is still farther strengthened by the almost 
indefinite length of time, during which, certain seeds re- 
tain their power of germinating; and certain animals, in a 
torpid state, the faculty of reviviscence. 
We are thus led from the phenomena which organized 
beings present, to reject the theory of equivocal genera- 
tion, and to admit the important conclusion of Harvey, 
Ez ovo omnia. But the manner in which these eggs or 
germs are produced, has furnished matter of curious spe- 
culation to the physiologist. By some, it has been sup- 
posed, that the germs of all the plants and animals that 
have been, or ever shall be, in the world, were really all 
formed within the first of their respective kind,—to be 
brought forth im a determinate order. This Theory of 
Evolution, as it has been termed, is in a great measure the 
result of microscopic observations, assisted by preconceived 
views. There is one circumstance, however, which not 
only receives no explanation upon the principles of this 
