MODERN BIOLOGY 469 



Upon the sexual organs. Here, too, reference is made to the varying results 

 to which different experiments have led. The fertility of variety-crosses, on 

 the other hand, is attributed to favourable conditions of variations in closely 

 related characters. The result of this is a proof that transition forms exist 

 between species and varieties. 



Darwin and Mendel 

 If we compare these discussions of Darwin's on heredity and hybridization 

 with the experiments that Mendel concurrently carried out for the same pur- 

 pose, the English scientist naturally gets left hopelessly behind — on his 

 part, widely vacillating speculations; on thepart of Mendel, clearly conceived 

 and exact experiments. The very starting-point brings this out clearly; 

 Mendel starts from a few simple and easily determined characters and es- 

 tablishes their appearance in different generations in various combinations; 

 Darwin, on the other hand, starts from the ideas of species and variety — 

 that is, from the most abstract terms in biology and the most difficult to 

 define. In fact, in this starting-point lies the whole weakness of Darwin's 

 research work and speculation. His successors, indeed, almost immediately 

 abandoned this standpoint and instead sought for proofs of their theory by 

 recourse to the material and methods of comparative anatomy; Cuvier and 

 his successors had already studied the changes undergone by one and the 

 same organ in a series of diff'erent animal forms. It was through this com- 

 parative method's being placed at the service of the theory of origin that 

 Darwinism, especially through Gegenbaur and his school, came to use for 

 purposes of investigation objects of a definite and concrete nature. But Dar- 

 win himself had but little mind for comparative anatomy; he certainly cites 

 for the purposes of his theory a number of proofs derived from morphology, 

 but in quite a brief and summary fashion. He was more interested in embry- 

 ology. Although he himself had never worked practically as an embryologist, 

 he nevertheless realized the value of comparative investigations into diff'erent 

 stages of development and he works out the basis for a "biogenetic prin- 

 ciple," which Fritz Miiller and Haeckel only had to supplement. 



Darwin on questions of geography 

 Darwin is, however, far more at home in the sphere of geology and geog- 

 raphy and he firmly rejects any attempts at employing the results of these 

 sciences to disprove his theory. The incompleteness of palasontological re- 

 mains he considers to be sufficient argument against those who inquire after 

 "missing links" between now existing genera and species, while the con- 

 ditions of distribution of living creatures seemed to him from the very out- 

 set to be the surest guarantee of the truth of his doctrine. Climatic changes 

 have in the course of the ages given the most powerful impulses both to new 

 variations and to the struggle for existence under new conditions, while 

 newly-formed natural barriers, mountain ranges and encroachments of the 



