EMBRYOLOG Y. 
135 
barous race, when subjected to more favorable conditions, 
in becoming more civilized, begin to resemble those more 
advanced,—considering these facts together, the view might 
be suggested to the Ethnologist that the different races 
سے 
had come from one stock. An important fact to be 
remembered in reference to the origin of races is that 
peculiarities which appear in the parent reappear in the 
offspring at the same age in which the parent was affected. 
Thus, the parent at a certain age develops a disease: his 
child grows up apparently healthy; suddenly the same 
disease appears in the child, and at the same age at which 
the parent was affected. Though the causes of peculiarities 
appearing in the parent, and the inheriting of them by the 
offspring, are still unknown, or very obscure, nevertheless 
we know it to be a fact that peculiarities—good or bad— 
affecting a parent may, and often do, reappear in the 
offspring in the manner just illustrated. Suppose, now, in 
a remote past, two animals, the descendants of the same 
parent, grew for some time alike, but that gradually they 
began to differ, acquiring certain peculiarities. These, if 
transmitted to posterity, would appear at the same age 
in which they were acquired by the parents. This hypo- 
thetical case illustrates what we suppose to have been the 
development of the Bird and Mammal from a common 
ancestor, the Reptile. This reptilian ancestor had two 
descendants; one acquired the peculiarities of the Bird, the 
other those of the Mammal: the Bird and Mammal of the 
present day ought, therefore, to develop in a reptilian 
manner until they attain the age at which their progenitors 
acquired the characteristic of the Bird and Mammal; from 
that time their development ought to be different. Our 
brief résumé of development shows that the facts perfectly 
confirm such a theory. By the same reasoning we con- 
clude that the Reptiles and Batrachia have diverged from 
a form like that of the Lepidosiren, or Mud-fish, the Bony 
