58 ZOOLOGICAL PHILOSOPHY 



in their characters ; and several have imagined that the affinities 

 among living beings may be represented something after the manner 

 of the different points of a compass. They regard the small well- 

 marked series, called natural families, as being arranged in the form 

 of a reticulation. This idea, which some modern writers think sub- 

 lime, is clearly a mistake, and is certain to be dispelled when we have 

 a deeper and wider knowledge of organisation ; and especially when 

 the distinction is recognised between what is due to the influence 

 of environment and habits and what is due to the greater or less 

 progress in the complexity or perfection of organisation. 



Meanwhile I shall show that nature, by giving existence in the course 

 of long periods of time to all the animals and plants, has really formed 

 a true scale in each of these kingdoms as regards the increasing com- 

 plexity of organisation ; but that the gradations in this scale, which 

 we are bound to recognise when we deal with objects according to 

 their natural affinities, are only perceptible in the main groups of the 

 general series, and not in the species or even in the genera. This 

 fact arises from the extreme diversity of conditions in which the various 

 races of animals and plants exist ; for these conditions have no relation 

 to the increasing complexity of organisation, as I shall show ; but they 

 produce anomalies or deviations in the external shape and characters 

 which could not have been brought about solely by the growing com- 

 plexity of organisation. 



We have then only to prove that the series constituting the animal 

 scale resides essentially in the arrangement of the main gi'oups com- 

 posing it, and not in that of species, nor always even of genera. 



The series to which I have alluded can then only be made out among 

 the larger groups ; since each of these groups, constituting the classes 

 and bigger famiUes, comprises beings whose organisation is dependent 

 on some special system of essential organs. 



Thus each distinct group has its special system of essential organs ; 

 and it is these special systems which undergo a degradation as we pass 

 from the most complex to the simplest. But each organ taken by 

 itself does not proceed so regularly in its degradations : and less so 

 in proportion to its lesser importance and greater susceptibility to 

 modification by environment. 



In fact, the organs that have httle importance or are not essential 

 to life are not always at the same stage of perfection or degradation ; 

 so that if we follow all the species of a class we shall see that some 

 one organ of any species reaches its highest degree of perfection, 

 while some other organ, which in that same species is quite un- 

 developed or imperfect, reaches in some other species a high state 

 of perfection. 



