CHAPTER VI. 



DEGRADATION AND SIMPLIFICATION OF OBGANISATION FROM 

 ONE EXTREMITY TO THE OTHER OF THE ANIMAL CHAIN, 

 PROCEEDING FROM THE MOST COMPLEX TO THE SIMPLEST. 



Among the problems of interest for zoological philosophy, one of the 

 most important is that which concerns the degradation and simpli- 

 fication observed in animal organisation on passing from one extreme 

 to the other of the animal chain, from the most perfect animals to 

 those whose organisations are the simplest. 



Now the question arises whether this is a fact that can be estabHshed ; 

 for, if so, it will greatly enhghten us as to nature's plan and will set 

 us on the way to discover some of her most important laws. 



I here propose to prove that the fact in question is true, and that 

 it is the result of a constant law of nature which always acts with 

 vmiformity ; but that a certain special and easily recognised cause 

 produces variations now and again in the results which that law 

 achieves throughout the animal chain. 



We must first recognise that the general series of animals arranged 

 according to their natural afi&nities is a series of special groups which 

 result from the difi'erent systems of organisation employed by nature ; 

 and that these groups are themselves arranged according to the de- 

 creasing complexity of organisation, so as to form a real chain. 



We notice then that except for the anomahes, of which we shall 

 ascertain the cause, there exists from one end to the other of this chain 

 a striking degradation in the organisation of the animals composing it, 

 and a proportionate diminution in the numbers of these animals' 

 faculties. Thus if the most perfect animals are at one extremity 

 of the chain, the opposite extremity will necessarily be occupied by 

 the simplest and most imperfect animals found in natirre. 



This examination at length convinces us that all the special organs 

 are progressively simpHfied from class to class, that they become 

 altered, reduced and attenuated little by little, that they lose their 



