65 
materials for the body of the young animal; and this is built 
up round a primitive groove, in the floor of which a notochord 
is developed. Furthermore, there is a period in which the 
young of all these animals resemble one another, not merely 
in outward form, but in all essentials of structure, so closely, 
that the differences between them are inconsiderable, while, in 
their subsequent course, they diverge more and more widely 
from one another. And it is a general law, that, the more 
closely any animals resemble one another in adult structure, 
the longer and the more intimately do their embryos resemble 
one another: so that, for example, the embryos of a Snake 
and of a Lizard remain like one another longer than do those 
of a Snake and of a Bird; and the embryo of a Dog and of a 
Cat remain like one another for a far longer period than do 
those of a Dog and a Bird; or of a Dog and an Opossum; 
or even than those of a Dog and a Monkey. 7 
Thus the study of development affords a clear test of close- 
ness of structural affinity, and one turns with impatience to 
inquire what results are yielded by the study of the develop- 
ment of Man. Is he something apart? Does he originate 
in a totally different way from Dog, Bird, Frog, and Fish, 
thus justifying those who assert him to have no place in nature 
and no real affinity with the lower world of animal life? Or 
- does he originate in a similar germ, pass through the same 
slow and gradually progressive modifications,—depend on the 
same contrivances for protection and nutrition, and finally 
enter the world by the help of the same mechanism? The 
reply is not doubtful for a moment, and has not been doubtful 
any time these thirty years. Without question, the mode of 
origin and the early stages of the development of man are 
identical with those of the animals immediately below him in 
the scale :—without a doubt, in these respects, he is far nearer 
the Apes, than the Apes are to the Dog. 
The Human ovum is about ;4; of an inch in diameter, and 
might be described in the same terms as that of the Dog, so 
that I need only refer to the figure illustrative (15 A.) of its 
F 
