ANIMAL KINGDOM. 287 



and I think that no better name can be adopted for this 

 new class. The word however is now taken in a wider 

 and even in a somewhat different sense from that in which 

 my learned friend applied it. For instance, it is not abso- 

 lutely meant that these animals do not undergo metamor- 

 phosis, but that, constructed on the same plan with the 

 larva? of true insects, they are rendered incapable by Na- 

 ture of completing their metamorphosis, and are able to 

 perform the offices of adult life in all the various stages of 

 an incomplete change of form. Such a species of imper- 

 fection is not unique, nor confined to the Annulosa ; for the 

 Ametabola have their prototypes among the Vertebrata 

 in the group of Amphibia, where the genera Siren and 

 Proteus are, to speak analogically, animals left imperfect 

 in the first stage of metamorphosis. On taking this view of 

 the subject, the class of Ametabola appeared to me to 

 consist of the five following orders, to one or other of 

 which we shall hereafter see that the larvae of insects may 

 be all assimilated : 



Vermes, 



Anoplura, 



Thysanura, 



Chilopoda, 



Chilognatha. 

 From the last of these, or the Chilognatha, we proceed 

 by the genus Glomeris to Oniscus, and thus enter among the 

 Crustacea, in some of which we discovera system of circu- 

 lation and respiration more analogous to that of the verte- 

 brated animals than to any thing among the Annulosa. On 

 leaving the Crustacea the next group of Annulose animals 

 appears to be the Arachnida, which, like some of the former, 

 have the head and thorax united into one piece. The 



