ANIMAL KINGDOM. 283 



ascertain the most natural groups into which the Annu- 

 losa may be distributed ; and having this object in view, the 

 following classes obviously occur to the mind as making a 

 very regular transition from one to the other : 



Myriapoda, 



Vermes, 



Insecta, 



Arachnida, 



Crustacea. 

 But however plausible this arrangement may appear at 

 first sight, it must not be forgotten that there are many ar- 

 ticulated animals which cannot without great violence be 

 made to enter into any one of these classes. Such for instance 

 are the Insecta Thysanura of Latreille, which though con- 

 sidered by all systematists as approaching near to the My- 

 riapoda must nevertheless be allowed by ever)' entomolor 

 gist to be more unlike to these, in some respects, than 

 even to certain Hexapod Insects. 



On looking back however towards the Fertebrata we may 

 perceive that there are few of their external organs so liable 

 to variation in form and number as those of locomotion. 

 Thus, whether our attention be turned towards the Reptilia, 

 Amphibia, or Fishes, we see in the same natural class some 

 animals with four feet ; some with two, and others, finally, 

 quite destitute of them. In the order of nature the Serpent 

 cannot be far separated from the biped lizard, nor this again 

 from the crocodile ; every part of their anatomy demon- 

 strates the truth of their belonging to the same natural 

 class. So far also as my examination of insects had gone, 

 I had always, on looking for natural characters, found those 

 taken from the organs of locomotion, whether wings or feet, 

 to be the most vague of any ; since these organs vary in the 



