OF THE ANNULOSA. 347 



When the external pair becomes null, we approach to the 

 Arachnida ; and when, on the other hand, the internal pair 

 gets indistinct, we may prepare ourselves for those Myri- 

 apod insects which form part of the class 



Ametabola. 



Every author on Entomology having observed the affi- 

 nity of the Oniscus Armadillo of Linnasus to the modern 

 genus Glomeris, it scarcely seems necessary to demonstrate 

 here the accuracy of that process of reasoning by which 

 the group of Ametabola is united to the Crustacea. It 

 may therefore suffice to say, that if the possession of four 

 antennae constitutes a general and absolute character of 

 the last-mentioned class, the genus Onhcus must cease to 

 belong to it on account of its having only a pair of these 

 organs. Now Degeer has observed that the young of 

 Oniscus Asellus L. or the genus Porcellio of Latreille, 

 on leaving the mother possess no more than six pair of 

 feet, and that as they advance in age they gain a segment 

 to their body, together with a pair of feet additional to 

 those which they possessed at their birth. This our ad- 

 mirable naturalist states to be an observation quite new, 

 and well worthy of attention. Such indeed it was in his 

 time, and even still remains ; for we shall perceive it to 

 form one of the many proofs, which, though now over- 

 looked, confirm that axiom which is alone sufficient to 

 immortalize its author, " Natura nonfacit saltus." 



In the first place, the genus Porcellio is justly referred 

 to the Crustacea by modern naturalists, because it breathes 

 by means of branchiae ; but when the form and the struc- 

 ture of its mouth and of its organs of locomotion only are 

 considered, the Latreillian order of C/iilognatha instantly 



