of previously unknown lands, as investigation became 

 more detailed and intensive, comparative anatomy arose 

 as an independent branch of zoology with distinct pur- 

 poses of its own; and it gained its specific form and char- 

 acter from the studies of the great zoologists of the early 

 nineteenth century Lamarck, Cuvier, Geoifroy St. Hi- 

 liare, Goethe, Owen, and Oken. These naturalists dis- 

 sected and compared the various organic systems of ani- 

 mals, following them as widely as possible from group to 

 group of the numerous vertebrate and invertebrate forms, 

 and they and their followers have placed the doctrine of 

 evolution upon the sure and broad foundation of com- 

 parative anatomy. The main principle of this department 

 of zoology is that the varied forms of animals exhibit 

 deep-seated likenesses that place them in groups related 

 to one another not as the rungs of a ladder as Lamarck 

 supposed, but rather as the branches of a tree or a bush; 

 and such branches again like those of a tree bear smaller 

 branches, and these reach to lesser or greater heights from 

 the base level of primitive organization. Thus, anatomy 

 holds that community of plan is an indication of genetic 

 affinities, while modifications of a common plan exhibit the 

 results of adaptation to different ends through evolution, 

 The framework of the human arm is constructed out 

 of the same elements with the same arrangement that 

 we find in the leg of a cat, the flipper of a seal, the paddle 

 of a whale, and even the wing of a bat, different though 

 these structures are in function, and in these resemblances 

 comparative anatomy discerns evidence of a remote com- 

 mon ancestry of men and whales and bats. 



Extended through the study of tissues, or histology, to 

 the unitary elements of organic structure the cells com- 

 parative analysis has brought the whole realm of organic 

 nature under the sway of a great principle the cell- 

 doctrine of the botanist Schleiden and the zoologist 



9 



