vi PREFACE. 



Even while limiting ourselves to this comparatively re- 

 stricted domain, we have had to consider, to group, to con- 

 dense and to classify, an enormous mass of facts derived 

 from all the natural sciences. Among these facts, numerous 

 as the stars of the heaven and the sands of the sea, we 

 have been compelled to make a choice, and to select as much 

 as possible what was most important, most significative, most 

 luminous. 



We hope that the learned men who devote themselves to 

 special subjects may find in our modest production some new 

 combinations, perchance some of those general views which 

 are sometimes lacking to certain men in other respects very 

 distinguished, but who abide too closely in this or that district 

 of knowledge, as happens often in this age when the division 

 of scientific labour is carried to excess. Nevertheless, we do 

 not write for scientific men. We wish especially to be read 

 by the mass of enlightened people, whom our very incom- 

 plete system of public instruction has left almost unacquainted 

 with Biology. In effect, our best establishments for secondary 

 instruction limit their ambition to imparting sufficiently 

 complete ideas of physics, and very incomplete ideas con- 

 cerning chemistry ; but they stop too timidly on the threshold 

 of Biology, the mysteries of which are accessible? only to a 

 small number of special men. This is a defect exceedingly 

 deplorable, exceedingly prejudicial to general progress. It is 

 on account of this defect that so many false and even 

 pernicious ideas continue to find acceptance and empire in 

 public opinion ; hence it is, in a great measure, that true 

 philosophy, or rather that philosophy which is alone solid 

 and sound, that which flows directly and legitimately from 



