INSECTA. 235 



which open and close, and beneath which, when at rest, the 

 wings are transversely folded. These scales or wing cases 

 are called elytra[l). The Insects provided with them are 

 named Coleoptera, and in such they are never absent, though 

 this is sometimes the case with respect to the wings. In other 

 Insects the extremity of the scale is completely membranous, 

 or like the wing : they are styled Hemiptera. 



The scutel or scutellum is usually a small triangular piece, 

 situated on the back of the mesothorax, and between the in- 

 sertions of the elytra or of the wings. Sometimes it is very 

 large, and then it covers the greater part of the superior por- 

 tion of the abdomen. In various Hymenoptera, behind the 

 scutellum and on the metathorax, we find a little space called 

 the post-scutellum. 



The ambulatory organs of locomotion consist of a coxa 

 formed of two pieces, ii femur, an uniarticulated tibia^ and of 

 a tarsus^ which is divided into several phalanges. The num- 

 ber of its articulations varies from three to five, a difference 

 which greatly depends upon the proportional changes expe- 

 rienced by the first and penultimate joints. Although their 

 supputation may sometimes prove embarrassing, and this nume- 

 rical series may not always be in exact accordance with the na- 

 tural order, it furnishes a good character for the distinction of 

 genera. Thelast joint is usually terminated by two hooks. The 

 form of the tarsi is subject to some modifications, according 

 to the habits of the animal. Those of aquatic species are 

 usually strongly ciliated and flattened, and resemble oars(2). 



The abdomen, which forms the third and last part of the 

 body, is confounded in the Myriapoda, with the thorax : but 

 in all other Insects, or those which have but six feet, it is dis- 

 tinct. It contains the viscera and the sexual organs, present- 

 ing nine or ten segments or annuli, some of which, however. 



(1) For their chemical composition, see Odier, Mem. cit , in the Mem. de la 

 Soc. d'Hist. Nat.; and the article Insectes of the same work. 



(2) M. Kirby, in his Monograph of the Bees of England, designates the two 

 anterior tarsi by the name of hands. The first joint is the palm, — palnia- This 

 gentleman, in conjunction with M. Spcnce, has published a very complete and 

 detailed work on the elements of Entomology. 



