CONSIDERATIONS. 11 



In the other orders of insects, the two segments which bear 

 the wings having ah-eady experienced a very considerable 

 change of form, it would require a more powerful cause to 

 bring them back to their primitive form : for this reason, the 

 return does not take place in Cimex celularius, the Formicse, 

 &c., amongst which the imperfection is only specific. In the 

 Aphaniptera, on the contrary, which we may consider as wing- 

 less Diptera, the transformation of the thorax takes place in 

 consequence of a complete absence of the wings, brought about 

 by the degradation which these organs have experienced in 

 passing through the whole of the Class Insecta. 



Seventh Law. — The form of many organs of the ver- 

 tebrata is generally in accordance with certain exterior agents, 

 to which they are connected by their function : in the Annu- 

 losa, this dependence is less rigorous, and sometimes even 

 insensible. 



Thus, in the former, the form of the teeth depends on the 

 species of aliment on which the animal feeds ; whilst, in the 

 latter, the organs of the mouth do not so rigorously follow the 

 same law, being often under the influence of a second function, 

 which modifies them, and causes them to appear anomalous. 

 For example ; we find in insects, carnivorous and herbivorous 

 species, which oflfer a very great resemblance in the masticatory 

 organs. In the Coleoptera, those which are the most carni- 

 vorous, such as the Carabi, the mandibles are commonly 

 elongate, and armed with very strong teeth, which serve 

 them as well to seize as to tear in pieces their prey ; whilst 

 their maxillae and labium are small and feeble. 



These characters are again found equally in Lucanus, which 

 lives only on the sap of trees ; but in these, the mandibles 

 serve more particularly for defence. Other insects offer, in 

 this respect, anomalies quite as remarkable. 



The aquatic habits of many insects often influence but 

 slightly the conformation, either of the whole body, or the feet 

 only. Insects never being entirely aquatic in the perfect state, 

 but only amphibious, it is not surprising that the feet of those 

 which commonly reside in water differ often but slightly from 

 those of the terrestrial species ; the form which they commonly 

 have, not being incompatible with the element in which the 

 insects reside. But the Crustacea, which are almost all 

 aquatic, offer very often, in their feet, forms which are nowise in 



