580 



INSECTA. 



oesophagus. The maxillary palps are as a rule rudimentary (except 

 in the Tineidce). When at rest the proboscis lies rolled up beneath 

 the mouth, and on either side of it are placed the large three- jointed 

 labial palps, which are often tufted with hairs and are situated on 

 the rudimentary triangular lower lip. 



The three thoracic rings are intimately fused with one another, and 

 like almost all external parts of the body are thickly covered with 

 hairs. The wings are in most cases very large, but in rare cases 

 are quite rudimentary (female Geometridce) ; the anterior are the 

 largest, and are distinguished by their partial or complete covering of 

 scale-like hairs which overlap one another in a tectiform manner, 

 and cause the extremely various colouring, tracing, and iridescence of 

 the wings. These scales consist of small, usually finely ribbed and 



toothed plates, which 



-A ^ Md \ are attached by styli- 



form roots in pores of 

 the integument of the 

 wings, and are com- 

 parable to flattened 

 out hairs. They arise 

 during the pupal 

 period. The arrange- 

 ment of the nervures 

 is of systematic value. 

 The essential arrange- 

 ment is a large median 

 cell near the root of 

 the wing, from which 

 six to eight radial 

 nervures pass to the 

 external lateral edges, while above and below the middle cell single 

 independent nervures run parallel to the upper or lower fringed 

 margin. The two pairs of wings are frequently connected with 

 one another by retinacula, the upper edge of the hind wings being 

 covered by spines or setae, which catch in a band of the anterior 

 wings. The legs are delicate and weak, their tibi are armed with 

 spurs of considerable size. The tarsuses are in general five-jointed. 

 The abdomen has six or seven segments and is thickly covered with 

 hairs, and ends not unfrequently with a strongly projecting tuft of 

 hairs. 



Nervous system. The brain is bi-lobed, and is provided with large 



FIG. 481. Mouth-parts of butterflies, (after Savigny) ; a, 

 of Zygcena ; I, of Noctua. A, Antennae ; Oc eyes ; Md, 

 mandibles ; Mxt maxillary palp ; MX, maxilla ; Lt, labial 

 palp ; Lr, labrum. 



