6 M. straus-durckheim's 



engaged on the important subject of classification : it is this — - 

 those genera which form the connecting links of the principal 

 divisions, offer, mostly, a very simple organization, which 

 scarcely teaches us anything of the structure of the families 

 which compose those divisions. 



In the Introduction, the author endeavours to explain the 

 laws which regulate the different changes of structure in 

 passing from one group to another. 



The most general law which we recognize in the organiza- 

 tion of animals is, that all the systems of organs * (" appareils") 

 are subjected to a constant variation of form, and even of 

 function, in passing from one family to another. 



In these changes, the organs mostly follow a gradation, by 

 which they arrive at a more perfect or imperfect state, according 

 to the plan which the Supreme Intelligence has ordained in 

 the creation of beings. Upon this depends the classification of 

 animals, at least the classification according to the System of 

 Nature. 



But however clear this law may be, in vain has been any 

 attempt to detect the principles on which it reposes ; and the 

 many different systems of classification which have been pro- 

 posed, show how great a diversity of opinion prevails on this 

 subject. But is not the principal cause of these varying 

 opinions, this — that most naturalists have founded their systems 

 on the supposed preeminence of some one particular organ, or 

 set of organs ; whilst no system can be in accordance with 

 nature, which does not rest on a consideration of the whole, 

 and on the greater or less degree in which each one influences 

 the other parts of the body ? 



Observation shows us that this general law is modified : 

 1. According to the functions which the organs have to per- 

 form: 2. According to the circumstances in which they are 

 placed, with regard to one another : and, 3. According as the 

 organs are, more or less, under the influence of external 

 causes. 



Consequently, this general law is divided into several par- 

 ticular laws (lois particulieres). To the examination of such of 



* I do not know how far I am correct in using this expression to convey the 

 same idea as the word " appareik," but I have been compelled to employ it, 

 not knowing any word in our language which conveys the precise meaning of 

 the French term. 



