18 



PRINCIPLES OF ANIMAL BIOLOGY 



molluscan type, the articulated type, and the radial type. He thus 

 arrived at a scheme of classification based upon similarity of structure, 

 which is even today the chief basis of classification. But curiously 

 enough, Cuvier failed to see what every zoologist now recognizes, that 

 similarity of structure is owing to common descent. He even used his 

 great powers of debate and his wide personal influence to combat the 

 idea of common descent. The general acceptance of the idea of evolution 

 was delayed many years by this error of Cuvier. 



Following Cuvier was a long line of able anatomists in the nineteenth 

 century, by whom comparative anatomy was raised almost to the rank 



Fig. 8. — Georges Cuvier, 1769-1832. {From Locy's Biology and Its Makers.) 



of an exact science. Their names are everyday words to the trained 

 morphologist, but no one of them stands forth preeminently, and they 

 need not be mentioned here. The later ones recognized common descent 

 as the key to similarity of structure, and comparative anatomy furnished 

 some of the best of the early evidence of evolution. 



The Discovery ot Cells. — Early in the nineteenth century, before 

 the end of Cuvier's career, the improvement of the microscope had 

 resulted in such excellence that the study of the minute anatomy of 

 animals and plants was becoming common among })iologists. A number 

 of investigators, some of them much earlier than the nineteenth century, 

 saw in organisms minute divisions, arranged sometimes in orderly manner, 

 sometimes in hit-or-miss fashion. Hooke saw box-like cavities in cork 

 as early as 1665, Malpighi a similar pattern in other plant tissues in 1670. 



