THE DEVELOPMENT THEORY. 



79 



Not that the opinions of the illustrious Englishman are yet 

 universally accepted; it has been recently seen with what 

 vehemence the defenders of the prevalent theory reject the 

 development hypothesis. But the appearance of the Darwinian 

 theory has excited long discussions ; to the arguments which 

 Lamarck formerly brought forward in favour of the vari- 

 ability of living beings, many others have been added by the 

 partizans of development. On the other side, the old doctrine 

 has been maintained with a passion which was little antici- 

 pated, so that at the present day, naturalists are divided into 

 two camps ; almost all who have devoted themselves to the 

 study of zoology or of botany have taken one side or the other. 



In one of these camps we find that the old school, those 

 who consider the organized world almost unchangeable, have 

 retrenched themselves. .According to them, the very numerous 

 series of animals and plants is limited to a certain number of 

 species, unalterable types which have the power of transmit- 

 ting themselves through successive generations, from their 

 origin to the end of time. It is scarcely admitted that the 

 species has the power of departing even slightly, and in a 

 temporary manner, from the primitive type. Those slight 

 changes, which are brought about by variations of climate or 

 of food, by domestication, or some other disturbing force of the 

 same order pass away when the species is again placed under 

 the normal conditions of its existence. The primitive type 

 then re- appears in its original purity. 



In the other camp the belief is entirely different ; the living 

 being is incessantly modified by the medium which it inhabits, 

 the temperature which it finds there, and the nourishment 

 which it procures. The habits which it is forced to assume 

 in order to live under new conditions cause it to acquire 

 special aptitudes which modify its organism, and change tlie 

 form of its body. And because hereditary descent transmits 

 to descendants, within certain limits, the modifications acquired 

 by their ancestors, the species is modified by degrees. Lamarck 

 was the author of this theory of development, to which Darwin 

 and his followers have recalled the attention of naturalists. 

 Darwin adds to these external influences, which can modify the 

 species of animals, another cause which maintains and increases 



