192 JOURNAL OF THE PLYMOUTH INSTITUTION. 
or unconsciously the address is a disquisition on Darwinism, or 
Darwinism illustrated by the development of the forms of animal 
life. Darwinism pushed to its ultimate conclusions, leads to the 
theory of Evolution, and we are not therefore surprised to find the 
learned President drawing the conclusion that ‘‘it is impossible for 
any one to be a faithful student of embryology, 7m the present state 
of science, without at the same time becoming an Evolutionist.” 
The saving clause of this judgment deserves, as it receives, our 
gratitude. As we look back on the past thirty or forty years, we 
can think of more than one exploded theory of which the same 
thing might have been said; theories on the nature of light, of 
heat, of electricity, of the origin of the primary rocks—so-called—of 
the constitution of the sun, and others. It may be quite as wise, 
and more philosophical, therefore, ‘‘in the present state of science,” 
to suspend judgment for awhile on the theory of Evolution, which 
is as yet scarcely twenty years old, lest, like one of olden time 
whose vision was still imperfect, we ‘‘see men as trees walking.” 
Dr. Thompson’s address may confirm the faith of those who have 
accepted the doctrine of Evolution, but there is nothing in it that 
obliges those to accept it who have hitherto been unable to adopt it. 
It is unnecessary, and it would be out of place to attempt, to 
analyze the address in detail, but there are two or three points in it 
which claim our attention. 
Dr. Thompson first traces the growth of plants by showing 
in a most interesting way that the essential part of the process 
of production is the formation of two cells of different kinds 
which, by themselves, have no power of further growth, but 
which by their union give rise to a product in which the power 
of development is raised to the highest degree; and that the two 
cells when united produce a mass usually spherical, which is the 
embryo of the future plant. Passing from plants to animals, he 
shows that the ovum, also more or less spherical in form, presents 
the essential characteristics of a complete cell, thereby establishing 
a strict analogy between the development of a plant and that of 
an animal. Dr. Thompson then anticipates any difficulty that may 
be found in the immense disparity of size in various animals, by 
showing that however much the mature animals may differ—as 
for example the elephant and the mouse, which in size are as 
150,000 : 1—yet there is scarcely any difference in the size of 
the ovum, and the same elementary structure is maintained in both. 
