126 SPECIES. 



always multiplying themselves with more or less regularity, 

 but so as to form an immense cone.* 



Each of these straight lines would represent a specific modi- 

 fication, accomplished after a certain number of generations 

 under the combined influence of the ambient medium and of 

 some considerable time : in other terms, each ramification 

 would represent a species having once existed or now exist- 

 ing on our planet. The length of each line would measure 

 the time which the species in question has existed. These 

 lines would never converge, because we do not believe in the 

 creation of permanent species by means of hybridity. 



Now the mind must admit here all possible combinations ; 

 certain species have disappeared without producing any others 

 after them : others exist actually without our having any idea 

 of one of the intermediary species which have been allied to 

 primitive species ; others have subsisted slightly or not at all 

 altered from the remotest antiquity up to our own days, thus 

 becoming through contemporaneous time the transformed 

 descendants of fossil species, of which they were also formerly 

 the contemporaries ; it is even not impossible but that certain 

 species succeeding one another may have presented a retro- 

 grade evolution, so that we must not always conclude that 

 because one animal is only inferior to another, it has therefore 

 preceded it : without going so far as all this, the evolution of 

 certain species may have presented a long time of cessation 

 whilst all others were progressing around them, so that they 

 appear to have retrograded. This is what has made M. 

 Micheletf say, " Nature has not progressed with a continuous 

 flow, but with retrograde movements, and stoppages, which 

 allow her to harmonise everything." These times of repose 

 in a specific evolution, as well as the hypothesis of successive 

 geneses which are already admitted, explain how the stratified 

 beds of the earth's surface, in showing from low to high what 

 we may call more perfect organic means, unveil at the same 



* The diagram which Darwin has placed in his book On the Origin of 

 Species, is only a fraction and piece of detail of the general figure which we 

 are endeavouring to place before the mind of the reader. 



t L'Insecte, p. 128, 1858. 



