226 BIOLOGY AND ITS MAKERS 
by emphasizing the factor of natural selection. The general 
acceptance of the doctrine, which followed after fierce oppo- 
sition, had, of course, a profound influence on embryology. 
The latter science is so intimately concerned with the gene- 
alogy of animals and plants, that the newly accepted doc- 
trine, as affording an explanation of this genealogy, was the 
thing most needed. 
The development of organisms was now seen in the light 
of ancestral history, rudimentary organs began to have 
meaning as hereditary survivals, and the whole process of 
development assumed a different aspect. This doctrine 
supplied a new impulse to the interpretation of nature at 
large, and of the embryological record in particular. The 
meaning of the embryological record was so greatly em- 
phasized in the period of Balfour that it will be commented 
upon under the next division of our subject. 
The period between Von Baer and Balfour proved to be 
one of great importance on account of the general advances 
in knowledge of all organic nature. Observations were 
moving toward a better and more consistent conception of 
the structure of animals and plants. A new comparative - 
anatomy, more profound and richer in meaning than Cu- 
vier’s, was arising. The edifice on the foundation of Von 
Bacr’s work was now emerging into recognizable outlines. 
THE PERIOD OF BALFOUR, WITH AN INDICATION OF PRESENT 
‘TENDENCIES 
Balfour’s Masterly Work.—The workers of this period 
inherited all the accumulations of previous efforts, and the 
time was ripe for a new step. Observations on the develop- 
ment of different animals, vertebrates and invertebrates, had 
accumulated in great number, but they were scattered 
through technical periodicals, transactions of learned societies, 
