226 BIOLOGY AXD ITS MAKERS 



by emphasizing the factor of natural selection. The general 

 acceptance of the doctrine, \Yhich followed after fierce oppo- 

 sition, had, of course, a ])rofound 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 sun'ivals, 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. Observ^ations were 

 nioving toward a better and m^orc consistent conception of 

 the structure of animals and plants. A new comparative 

 anatomy, more profound and richer in meaning than Cu- 

 \ier's, was arising. The edifice on the foundation of Von 

 Baer'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, 



