SUMMARY OF 'PHILOSOPHIE ZOOLOGIQUE? 273 



" We must, therefore, either give up the belief of 

 the universal sterility of species when crossed, or we 

 must look at this sterility in animals, not as an inde- 

 lible characteristic, but as one capable of being removed 

 by domestication. 



" Finally, on considering all the ascertained facts on 

 the intercrossing of plants and animals, it may be con- 

 cluded that some degree of sterility, both in first 

 crosses and in hybrids, is an exceedingly general result, 

 but that it cannot, under our present state of knowledge, 

 be considered as absolutely universal." * 



Returning to Lamarck, we find him saying : 



" The limits, therefore, of so-called species are not so 

 constant and unvarying as is commonly supposed. 

 Consider also the following. All living forms upon the 

 face of the globe have been brought forth in the course 

 of infinite time by the process of generation only. 

 Nature has directly created none but the lowest organ- 

 isms ; these she is still producing every day, they being, 

 as it were, the first sketches of life, and produced by 

 what is called spontaneous generation. Organs have 

 been gradually developed in these low forms, and these 

 organs have in the course of time increased in diversity 

 and complexity. The power of growth in each living 

 body has given rise to various modes of reproduction, 

 and thus progress, already acquired, has been preserved 

 and handed down to offspring.! With sufficient time, 

 favourable conditions of life [circonstances], successive 

 changes in the surface of the globe, and the power of 

 new surroundings and habits to modify the organs of 

 * Origin of Species,' p. 241. t ' Phil. Zool.,' p. 82. 



T 



