THE NATURALIST S OCCUPATION. 35 



found ascending grades of organization in the vertebrates 

 of the present ; paleontology discovered a corresponding 

 gradation in the vertebrates of the past ; and embryology 

 revealed the same serial gradation in developmental 

 stages. The discovery of this most remarkable parallel- 

 ism between the three series, the anatomical, the pale- 

 ontological, and the embryological, is one of the most 

 brilliant in the whole history of biology, and one which 

 with pride and admiration we place to the credit and 

 honor of Louis Agassiz. It is remarkable that these 

 three of the leading biologists of the century, after 

 laying the foundation of the theory of transformation, 

 remained to the end its most determined opponents. It 

 was left for Charles Darwin to show that the coincidence 

 pointed out by Agassiz between the geological succes- 

 sion, the embryonic development, and the zoological 

 gradation, held also in the geographical distribution of 

 animals in the past and the present, and to find the 

 interpretation of the fact now universally accepted. 



The recognition of so fundamental a truth as that of 

 community of descent, at once raised every department 

 of biology to a new plane, gave new aims to each, and 

 profoundly altered their relations to each other. Descent 

 was seen to be ''the hidden bond of connection " so lona: 

 sought for under the '' natural system " of classification. 

 Embryonic development came to be regarded as the 

 epitomized history of ancestral development. As Dar- 

 win puts it, the embryo is "a picture, more or less 

 obscured, of the progenitor, either in its adult or larval 

 state, of all the members of the same great class." 



'' In two or more groups of animals, however much 

 they may differ from each other in structure and habits 



