OF SPECIES 45 



are no longer extant in nature : this however is nothing more than 

 a possibiHty. 



But animals living in the waters, especially the sea waters, and 

 in addition all the races of small sizes Hving on the surface of the earth 

 and breathing air, are protected from the destruction of their species 

 by man. Their multiplication is so rapid and their means of evading 

 pursuit or traps are so great, that there is no likelihood of his being 

 able to destroy the entire species of any of these animals. 



It is then only the large terrestrial animals that are liable to exter- 

 mination by man. This extermination may actually have occurred ; 

 but its existence is not yet completely proved. 



Nevertheless, among the fossil remains found of animals which 

 existed in the past, there are a very large number belonging to animals 

 of which no hving and exactly similar analogue is known ; and among 

 these the majority belong to molluscs with shells, since it is only the 

 shells of these animals which remain to us. 



Now, if a quantity of these fossil shells exhibit differences which 

 prevent us, in accordance with prevailing opinion, from regarding 

 them as the representatives of similar species that we know, does it 

 necessarily follow that these shells belong to species actually lost ? Why, 

 moreover, should they be lost, since man cannot have compassed their 

 destruction ? May it not be possible on the other hand, that the fossils 

 in question belonged to species still existing, but which have changed 

 since that time and become converted into the similar species that we 

 now actually find. The following consideration, and our observations 

 throughout this work, will give much probability to such an assumption. 



Every quahfied observer knows that nothing on the surface of the 

 earth remains permanently in the same state. Everything in time 

 undergoes various mutations, more or less rapid according to the 

 nature of the objects and the conditions ; elevated ground is 

 constantly being denuded by the combined action of the sun, rain- 

 waters and yet other causes ; everything detached from it is carried 

 to lower ground ; the beds of streams, of rivers, even of seas change 

 in shape and depth, and shift imperceptibly ; in short, everything on 

 the surface of the earth changes its situation, shape, nature and appear- 

 ance, and even climates are not more stable. 



Now I shall endeavour to show that variations in the environment 

 induce changes in the needs, habits and mode of life of living beings, 

 and especially of animals ; and that these changes give rise to modi- 

 fications or developments in their organs and the shape of their parts. 

 If this is so, it is difficult to deny that the shape or external characters 

 of every hving body whatever must vary imperceptibly, although 

 that variation only becomes perceptible after a considerable time. 



