INSECTA. 347 



But this binary division is insufficient for the general propositions 

 which the comparative anatomist has to enunciate ; and I take, 

 therefore, the third kind of characters, the value of which was first 

 fully discerned by Linnaeus, viz., that founded upon the organs of 

 flight. Those Hexapod Insects which are devoid of wings are called 

 Aptera ; those with two wings only are the Diptera. All the rest 

 have four wings. The Lepidoptera have four scaly wings ; the 

 Hijme7ioptera have four veined wings, crossing each other when at 

 rest ; the Hemiptera have one pair of wings partially thickened, and 

 called hemelytra ; the Orthoptera have one pair of wings wholly 

 thickened, the other folded lengthwise ; the Coleoptera have one pair 

 wholly and much thickened, called elytra, and the other pair folded 

 crosswise ; the Neuroptera have four reticulated wrings ; the Stre- 

 psiptera have one pair of wings rudimental and curled up. In the 

 Aphaniptera both pairs are rudimental and functionless as wings. 

 Of these orders the first five are " haustellate ; " the next four 

 are " mandibulate." The Aptera are ametabolian ; the Hemiptera 

 and Orthoptera are hemimetabolian ; the remaining orders are " me- 

 tabolian." These characters, therefore, briefly and succinctly express 

 the highest generalisations, as yet reached, relative to the Hexapod 

 Insecta. 



Although, typically, the Hexapods have thirteen segments, in 

 the last stage of the metabolian orders, one, two, or three segments 

 may become blended together; and although we reckon the head 

 as a single segment, the number of jointed appendages which it 

 supports, under the name of antennae, mandibul^, maxillae, palpi, &c., 

 indicates that here, as in the Crustacea, it consists essentially of 

 several coalesced segments. 



With regard to the orders of the Myriapoda, the Chilognatha have 

 two biarticulate mandibles, without palpi, armed with imbricated 

 teeth planted in a cavity at the upper extremity of the mandible ; 

 they have also a kind of lip situated immediately beneath, and 

 covering the mandibles, notched into four divisions, and answering 

 to the two pairs of maxillae of the Crustacea ; whence the name from 

 the Greek, signifying, " feeding by jaws." The lulus, or Gally- 

 worm (Jig. 140), is a tjpe of this order. The Chilopoda have the 

 mouth composed of two mandibles, with a small palp ; a quadrifid 

 lip, also the homologue of the crustaceous maxillae confluent ; two 

 labial palpi, hooked at the tip; and a second pair of jaws, or foot 

 jaws, — the obvious homotypes of feet, — terminated by a strong 

 hook, moveable, and pierced beneath the extremity by a poison- 

 duct. The Centipede {Scolopendra) is the type of this order of 

 Myriapods, which "feed by feet." 



