AFFINITIES AND ANALOGIES OF ORGANIZED BEINGS. 221 



by man in detecting it ; for it is no more to be expected that 

 systematists should have already unravelled all the resem- 

 blances between species contemplated by the Creator, than 

 that anatomists should have arrived at the final cause of every 

 organ of the human body. The variety of classifications 

 adopted by different naturalists, shows that we are still far 

 from the true system of Nature, yet I think there can be no 

 doubt that naturalists have already sketched out its principal 

 features with considerable accuracy. Who, for instance, can 

 doubt that such groups as Vertebrata, Insecta, Mammalia, 

 Pisces, Coleoptera, &c., are not merely human generaliza- 

 tions, but real apartments in the edifice of the Divine Archi- 

 tect ? It is not, however, sufficient, that man should detect 

 these natural groups,— he must also give a definition of their 

 characters,— not of the superficial and arbitrary ones, but 

 of the essential and important, and this is often the most 

 difficult part of his task. Although these essential charac- 

 ters form the groundwork of the natural system, yet no rule 

 can apparently be laid down for their determination in par- 

 ticular cases. All that man can do is to use his best judg- 

 ment in selecting such characters for a group, as seem to him 

 the most important in their influence on the vital functions 

 of the beings which compose it. They must, in great mea- 

 sure, be left to the determination of what Linna)us called a 

 " latent instinct" which Professor Whewell defines to be " an 

 unformed and undeveloped apprehension of physiological 

 functions.^" 



When by these considerations we have amved at the no- 

 tion of a natural system, composed of natural groups arranged 

 in a determinate order, we may proceed to define affinity as 

 the relation which subsists between two or more members of 

 a natural group, or in other words, an agreement in essen- 

 tial characters. After the essential characters of such a 

 group have been discovered and defined, then all the objects 

 which possess those essential characters are said to have an 

 affinity for one another. Hence we see why the idea of a 

 natural system is necessary to the definition of affinity, for 

 in an artijicial system the characters of the groups are not 

 essential, but arbitrary, and the relation between the mem- 

 bers of such a group w^ould be, not affinity, but mere resem- 

 blance or analogy. Thus, if an author were to establish the 

 characters of the class Visce^, not on the essential characters 

 derived from the circulatory system, but on the arbitrary one 

 of being adapted for swimming, he would then include the Ce^ 



* History of tlie Inductive Sciences, vol. iii. p. 312. 



