EVOLUTION AS SEEN IN THE STRUCTURE OF MODERN ANIMALS 



35 



piercinq 

 bristles 



palps of 

 si maxilla 



labrum 

 hvpopharynx 



Znd maxillci 



HOUSE FLY 



labrum 



tube for 

 saliva 



palps of 

 2ncl maxilla 



mandible 



1st maxilla 



proboscis 

 (1st maxillae) 



BUG 



BUTTERFLY 



FIG. 3.9. Mouth parts of bug, house fly, and butterfly. Upper drawing of the bug shows 

 the beak attached to the head, with only the tips of the piercing bristles showing. Lower 

 drawing shows a portion of the beak cut away to reveal the cross section, with on en- 

 larged cross section of the bristles at the right. Mandibular bristles shown in diagonal 

 shading; 1st maxillary bristles, solid block; 2nd maxillae, forming the beak, unshaded. 



elongated, hollowed out on their adjoining surfaces, and held together by 

 interlockino grooves and ridges. Mandibles and 2nd maxillae are rudimen- 

 tary, except in one family of moths which have retained biting mouth 

 parts, thereby adding evidence in support of the view that sucking mouth 



