OF INSECTS. 297 



the Hymenoptera from the rest of their class, but 

 it is necessary to describe the various parts more in 

 detail. 



The head is not received into a cavity of the thorax, 

 but is attached to it by a ligament, so flexible that 

 the head can be almost turned round upon it. It 

 is likewise capable of some extension, and the head 

 has thereby considerable freedom of motion. The 

 composite eyes are sometimes larger in the males 

 than in the other sex. The stemmata are always 

 three in number, commonly disposed in an equilateral 

 triangle, but occasionally almost in a transverse line. 

 In the organs of the mouth we can distinctly recog- 

 nise mandibles, maxillae, lingua, labrum, labium, and 

 palpi ; but these parts are so variously modified in 

 different tribes, that a general definition of them will 

 possess little value. The mandibles are strong and 

 salient, usually toothed, and sometimes each blade 

 appears as if formed by the union of two similar 

 pieces. The maxillae are usually much developed, 

 the blade or stipes often greatly elongated, and the 

 insertion (the cardo or hinge of Kirby,) distinctly 

 visible. The blade of the maxillae acts an important 

 part in composing the tube in honey-sucking tribes. 

 There are commonly two lobes at the extremity, 

 which are sometimes acute, at other times very ob- 

 tuse. The palpi attached to this blade are almost 

 always long, and in the greater number of instances 

 contain six joints ; in the minute parasites, however, 

 they are frequently abnormal, and often present only 

 two articulations. The labium is much larger than 



