154 CLASS INSECTA. 



THE FOURTH ORDER OF INSECTS. 



The Suctoria De G. — Siphonaptera, Leach, 



Which composes the last of the apterous insects, have for 

 mouth, a sucker of three pieces,* enclosed between two arti- 

 culated laminse, forming, Avhen united, a proboscis or bill, 

 either cylindrical or conical, and the basis of which is covered 

 by two scales. These characters exclusively distinguish this 

 order from all others, and even from the hemiptera, to which 

 it approximates the most under these relations, and in which 

 Fabricius has placed the present insects. The suctoria, 

 moreover, undergo true metamorphoses, analogous to those 

 of many insects with two wings, as for instance, the tipu- 

 laria. 



This order is composed but of a single genus, that of 



The Fleas (Pulex L.), 



Their body is oval, compressed, clothed Avith a skin of 

 sufficient firmness, and divided into twelve segments, four of 



* Roesel represents but two ; but M. M. Kirby and Straus have ob- 

 served an additional one. According to the latter, the two scales cover- 

 ing the basis of the bill are palpi. 



