340 THE HISTORY OF BIOLOGY 



the last mammal in the series is more perfect than the first bird. Here Cuvier 

 has certainly laid his finger on one of the weakest points of the whole series- 

 theory, as expounded by Bonnet and Lamarck, and has undeniably fore- 

 stalled the conception of the relativity of the degree of evolution as held in 

 modern times. And as an application of this doctrine of his he presents his 

 famous type-grouping system. According to this, the animal kingdom is di- 

 vided into four main groups, Vertebrata, Mollusca, Articulata, and Radiata. 

 Within each of these groups there is a special "ground-plan" for the con- 

 struction of the life-forms — a plan that appears modified in various ways 

 in the different systematic categories within the type. Thus, the animals 

 within the same type may be compared with one another, but there is no 

 comparison between the ground-plans of the different types. This type theory 

 is Cuvier's greatest contribution in the sphere of systematization and repre- 

 sents the farthest advance in animal classification since Linnasus; in fact, 

 it represents, although in a somewhat modified form, the basis of all sub- 

 sequent animal classification, and it is thanks to it that modern biology has 

 been able to lay firmer foundations for the theory of descent than Lamarck 

 succeeded in doing with his uniform evolutional series. But this is certainly 

 due to the fact that in modern times it has been possible to compare ground- 

 plan and organic structure even in animals belonging to different types. Here 

 Cuvier was far too reluctant, as indeed he was in the application of his geo- 

 logical theory, to draw his conclusions from the observations on which he 

 based his system. 



Besides the account of the type theory, the work in question also con- 

 tains a number of observations on general scientific problems, and here, as 

 everywhere, Cuvier maintains the strictly critical attitude which to him 

 was one of the essentials of life. He is a master in not giving utterance to 

 more than he can stand for, and sometimes it is only in a roundabout way 

 that one can guess his train of thought. Thus, he repeats his above-mentioned 

 principle regarding life's quality of counteracting the manifestations of chem- 

 ical affinity in the elements that form the body, and he adds that it would 

 be irrational to assume that the force which acts in that way has a chemical 

 nature. But he enunciates no definite vitalistic theory. With equal caution 

 he expresses himself in regard to fertilization; how the embryo arises we 

 cannot tell, we can only study its subsequent development. Similarly, the 

 essence of the soul-life is a mystery; materialism is an arbitrary hypothesis, 

 "so much the more so as philosophy cannot offer any direct proof of the 

 true existence of matter." Here Cuvier has undoubtedly learnt from Kant; 

 on the other hand, his analysis of the influence of sense-impressions upon 

 the brain seems rather to have been influenced by Condillac and his school. 

 However, the knowledge with which Cuvier applies the theories of the new 

 chemistry to zoology represents a remarkable advance; in this respect 



