INSECTS 



3" 



anterior termination of the body, and is surrounded by the so-called 

 mouth parts (see Section 3), or oral appendages. These, in order to 

 perform their work effectually, require firm supports, and the muscles by 

 which they are set in motion must have firm points of attachment. Both 

 these conditions are satisfied by the coalescence of several (four) of the 

 somites into a firm capsule, the head. The three succeeding somites 

 carry the organs of locomotion, viz., the three pairs of legs on their 

 under surface, and in 

 the majority two pairs 

 of wings attached to the 

 dorsal surface of the last 

 two somites. The same 

 conditions, however, ap- 

 ply to the locomotive 

 organs, especially the 

 wings (compare with the 

 breast of birds), as have 

 been mentioned in the 

 case of the mouth parts ; 

 and accordingly these 

 somites likewise, wholly 

 or partially, coalesce into 

 a single division, the 

 thorax. (Why have larvae 

 no special thoracic 

 region?) In the third 

 division of the body, the 

 abdomen, the separate 

 rings are quite distinct 

 from each other, neither 

 limbs nor wings being 

 developed in this region. 



2. Organs of Loco- 

 motion. — These, as we 

 have seen above, consist 

 of legs and wings. 



(a) Of the legs, three 

 pairs are always present on the lower surface of the thoracic segments. 

 They are thus placed below the centre of gravity of the body, a position 

 by which rapidity and sureness of the animal's movements is secured. 

 The limbs being invariably directed obliquely outwards, the insect, 

 whether standing or running, always rests upon a large surface of 



Divisions of the Body of an Insect, with Respira- 

 tory and Nervous Systems (Diagrammatic). 



1. Divisions of the Body : K. , Head with (A. ) eyes ; F. , an- 

 tennse ; M., mouth parts; B., thorax (the edges of the 

 separate segments composing it still visible) with the three 

 pairs of legs and two pairs of wings ; H., coxa ; Sr., tro- 

 chanter ; S., femur ; Sch., tibia ; F., tarsus with two ter- 

 minal claws ; H., abdomen. 



2. Respiratory System : L., Tracheas ; Al., stigmata. 



3. Nervous System: Nk., Nervous ganglia ; Ns., nerve cords ; 

 uS., inferior oesophageal ganglion; oS.. superior oesopha- 

 geal ganglion, from which nerves pass off to A., the eyes,, 

 and F. , the antennae. 



