ZOOGENESIS 



entity. Rather a species is to be regarded as a re- 

 strained and repressed force — an enigmatic potenti- 

 ality — which, once released, will go to unknown and 

 unsuspected lengths. 



The peculiarities of species are best appreciated 

 through the consideration of a few examples taken 

 more or less at random from the animal world. 



Some species are constant in their characters and 

 practically invariable. Thus wherever it is found the 

 American eel is always the same. There is no differ- 

 ence between Canadian and West Indian or Brazilian 

 specimens. It is very closely related to the similarly 

 constant European eel, from which it differs in having 

 about seven less vertebrae in its backbone. The breed- 

 ing ranges of the American and of the European eels 

 broadly overlap, yet no American eel has ever been 

 taken in Europe and no European eel has ever been 

 taken in America. Although these eels are so very 

 closely related the American eel passes through its 

 larval stage in rather less than a year, while the larval 

 stage of the European eel occupies from two to 

 three years. 



Among the butterflies the common painted lady, 

 which is found throughout the world except in the 

 polar regions, Australia and New Zealand, and South 

 America south of the northern coast, is also every- 

 where the same. It shows temporary and individual 

 variations resulting from temporary local factors, but 

 no permanent local variation. The same is the case 

 with the red admiral which is found in western 

 Europe and over a large part of North America, and 



