ANNULOSA I INSECTA. 269 



thorax," " mesothorax," and "m eta thorax/' and each bears a 

 pair of jointed legs. In the great majority of Insects, the 

 dorsal arches of the mesothorax and metathorax give origin each 

 to a pair of wings. 



Each leg consists of from six to nine joints. The first of 

 these, which is attached to the sternal surface of the thorax, is 

 called the " coxa/' and is succeeded by a short joint, termed 

 the " trochanter." The trochanter is followed by a joint, often 

 of large size, called the "femur," and this has articulated to it 

 the " tarsus," which may be composed of from two to five 

 joints. 



The wings of Insects are membranous " flattened vesicles, 

 sustained by slender but firm hollow tubes, called ' nervures/ 

 along which branches of the tracheae and channels of the 

 circulation are continued " (Owen). According to New- 

 port, the wings of Insects are " expanded portions of the 

 common integuments of the sides of the meso- and meta- 

 thorax, occasioned by the enlargement and extension of 

 numerous tracheae and the accompanying passages for the 

 circulatory fluids, and their motions are intimately connected 

 with the function of respiration." In the Coleoptera (Beetles) 

 the anterior pair of wings become hardened by the deposition 

 of chitine, so as to form two protective cases for the hinder 

 membranous wings. In this condition the anterior wings are 

 known as the "elytra," or "wing-cases." In some of the 

 Hemiptera this change only affects the inner portions of the 

 anterior wings, the apices of which remain membranous and to 

 these the term " hemelytra " is applied. In the Diptera the 

 posterior pair of wings are rudimentary, and are converted into 

 two capitate filaments, called "halteres," or "balancers." In 

 the Strepsiptera the anterior pair of wings are rudimentary, and 

 are converted into twisted filaments. 



The primitive number of somites in the abdomen of insects 

 is said to be eleven (Orthoptera), but nine is the number ordi- 

 narily present ; and though these are distinct in most larvae, it is 

 seldom that more than seven or eight are recognisable in the 

 adult. The abdominal somites are usually more or less freely 

 movable upon one another, and never carry locomotive limbs. 

 The extremity of the abdomen is, however, not infrequently 

 furnished with appendages, which are connected with the 

 generative function, and not infrequently serve as offensive 

 and defensive weapons. Of this nature are the ovipositors of 

 Ichneumons and other insects, and the sting of Bees and 

 Wasps. In the Earwig (Forficula) these caudal appendages 

 form a pair of forceps ; whilst in many Insects they are in the 



