THE EVOLUTION OF LIKE 



I need only point to one of its most successful depart- 

 ments, the skeleton of the vertebrates, the comparison 

 of the various forms of the skull, the vertebral column, 

 the limbs, etc. It is not in vain that for more than a 

 hundred years gifted scientists, from Goethe and Cuvier 

 to Huxley and Gegenbaur, have devoted years of 

 laborious research to the methodical comparison of 

 these similar yet dissimilar forms. They have been 

 rewarded by the discovery of the common laws of 

 structure, which can only be explained in the sense of 

 modern evolution by descent from common ancestors. 



We have a striking example of this in the limbs of 

 mammals, which, with the same internal skeletal struct- 

 ure, show a very great variety in outer form — the 

 slender bones of the running carnivora and ungulates, 

 the oar-bones of the whale and seal, the shovel-bones of 

 the mole and hypudasus, the wings of the bat, the climb- 

 ing bones of the ape, and the differentiated limbs of the 

 human body. All these different skeletal forms have 

 descended from the same common stem-form of the 

 oldest Triassic mammals; their various forms and 

 structures are adapted in scores of ways to different 

 functions; but they rise tJirough these functions, and all 

 these functional adaptations can only be understood by 

 progressive heredity. The theory of germ-plasm gives 

 no causal explanation whatever of them. 



The majority of recent biologists are of opinion that of 

 the two chief constituents of the nucleated cell the cyto- 

 plasm of the cell-body discharges the function of nutri- 

 tion and adaptation, while the caryoplasm of the nucleus 

 accomplishes reproduction and heredity. I first advanced 

 this view in the ninth chapter of the General Morpltoloiiy 

 (in 1866); and it was afterwards solidly and empirically 

 established by the excellent investigations of Eduard 

 Strasburger, the brothers Oscar and Richard Hcrtwig, 

 and others. The elaborate finer structures which these 



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