1 1 2 PIONEERS OF E VOL UTION. 



is apparent in his writings, led him to reject the cur- 

 rent behef in the separate creation of species. He 

 saw that this theory wholly failed to account for the 

 existence of abnormal forms, of adaptations of the 

 structure of organs to their work, of gradations be- 

 tween living things, and other features inconsistent 

 with the doctrine of " let lions be, and there were 

 lions." His shrewd comment on the preformation 

 notion of development has been quoted (p. 20). 

 The substance of his argument in support of a 

 " physical basis of life " is as follows : " When we 

 revolve in our minds the metamorphosis of animals, 

 as from the tadpole to the frog; secondly, the changes 

 produced by artificial cultivation, as in the breeds 

 of horses, dogs, and sheep ; thirdly, the changes pro- 

 duced by conditions of climate and of season, as in 

 the sheep of warm climates being covered with hair 

 instead of wool, and the hares and partridges of 

 northern climates becoming white in winter; when, 

 further, we observe the changes of structure pro- 

 duced by habit, as seen especially by men of differ- 

 ent occupations; or the changes produced by arti- 

 ficial mutilation and prenatal influences, as in the 

 crossing of species and production of monsters; 

 fourth, when we observe the essential unity of plan 

 in all warm-blooded animals — we are led to con- 

 clude that they have been alike produced from a 

 similar living filament." The concluding words of 

 this extract make remarkable approach to the mod- 

 ern theory of the origin of life in the complex jelly- 



