VI teanslatob's pbeface. 



termed laws. By the operation of these, or some 

 suck processes, have men been enabled to form all 

 those general conclusions, which constitute the founda- 

 tion of each branch of the natural sciences. It is, 

 however, unhappily the case, that biology stands, in 

 this aspect, lowest in the scale ; for not only has the 

 difficulty in carrying out experimentation been an 

 obstacle of a very formidable character, but it has 

 been customary among its devotees to arrive at fixed 

 conclusions from very uncertain premisses. Hence the 

 laws which control life in its widest limits have ever 

 been imperfectly defined ; and although Nature's 

 statute-book has a certain existence, those of its 

 leaves which have fallen into human hands have been 

 so fragmentary, that at present we may safely aver, in 

 the language of a celebrated anatomist, that "the 

 known is very small compared with the knowable." 



Such being the state of things, our deepest gra- 

 titude is due to the man who, uniting the results of 

 his own inquiries to those acquired by the investiga- 

 tions of others, and lending a clear mind to the 

 analysis of the whole, sketches for us even the rude 

 and imperfect outlines of that plan upon which force 

 is permitted to labour in the production of living 

 beings. Professor De Quatrefages is the person to 

 whom we owe our thanks ; for, in the present volume, 



