18 CLASS INSECTA. 



The limbs are composed of a haunch with two articula- 

 tions, of a thigh, of a leg, with a single articulation, and of 

 a toe which is usually named tarsus, and which is divided 

 into several phalanges. The number of its articulations 

 varies, from three to five, which depends much on the 

 changes which the first and the last but one undergo in their 

 proportion. Although their calculation may sometimes 

 embarrass, and this numerical series is not always in rela- 

 tion with the natural order, it nevertheless furnishes a good 

 character for the distinction of genera. The last articula- 

 tion is commonly terminated by two crotchets or hooks. The 

 form of the tarsi is subject to some modifications, according 

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

 usually flatted, much ciliated or provided with small hairs, 

 and in the form of oars.* 



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

 body, is confounded with the corslet, in the myriapods — but 

 it is distinct from it in all other insects, or those which have 

 but six feet. It encloses the viscera, the sexual organs, and 

 presents from nine to ten segments, some of which, how- 

 ever, are often concealed, or very much abridged. The 

 parts of generation are situated at its posterior extremity, 

 and issue through the anus. The iuli and libellulae alone 

 form an exception to this. The last rings of the abdomen 

 form, in many females, an oviduct, which is retractile, or 

 always projecting, more or less complicated, and serving 

 the purpose of an auger. It is replaced by a sting in most 

 of the females of the hymenoptera. The fecundating 



* Mr. Kirby, in his Monograph of English Bees, denominates the two 

 anterior tarsi, hands. The first articulation is the palm. In conjunction 

 with Mr. Spence he has published the Elements of Entomology in a very 

 detailed and complete style. 



