ARTHROPODA. 99 



Class V. Insecta (Hexapoda). 



Tracheates with distinct head, thorax and abdomen. The head bears 

 a pair of antennae, compound eyes, palpless mandibles, and two other 

 pairs of jaws ; the three thoracic segments bear three pairs of legs, and 

 commonly one or two pairs of wings; abdomen usually limbless. At 

 most ten pairs of stigmata. Sexes separate. 



A. INCOMPLETE METAMORPHOSIS. 



Order 1. Orthoptera. Jaws adapted for biting; two pairs of dissimilar 

 wings. Forficula, earwig. Periplaneta (Blatta) orientalis, cock- 

 roach. Phyllium, Phasma, Bacteria calamus, and Mantis religiosa 

 exhibit mimicry. (Edipoda migratoria, passage locust, Locusta 

 viridissima, grasshopper. Gryllotalpa vulgaris, mole-cricket, Gryllus 

 campestris, GK domesticus, house-cricket. 



Order 2. Thysanura (Aptera), wingless. Body hairy or scaly. Mouth- 

 parts rudimentary. Tracheae may be absent. Podura. Lepisma 

 saccharina. Campodea staphylinus with foot-stumps on the anterior 

 abdominal segments. 



Order 3. Pseudoneuroptera. Mouth-parts biting; wings membranous, 

 alike. Termes lucifugus, white ant. Thrips. Amphibiotic forms 

 (the larvae aquatic, with tracheal gills): Ephemera vulgata, May-fly. 

 Agrion puella, -ffischna grandis, Libellula vulgata, dragon flies. 



Order 4. Hemiptera. Mouth-parts piercing or sucking. Coccus cacti, 

 cochineal insect, on Opuntia. Aspidiotus nerii, on Oleander. Aphis 

 rosae with two honey-tubes ; parthenogenesis in spring and summer. 

 Phylloxera vastatrix, vine-louse, (from the winter-eggs wingless forms 

 emerge in the spring, which destroy the vine-roots and reproduce par- 

 thenogenetically; later generations cause leaf -galls; the winged genera- 

 tion of late summer produce, parthenogenetically, dimorphic eggs from 

 which large females and small asplanchnic males are hatched). Cicada, 

 the abdomen of the male with a stridulating organ. Acanthia (Cimex) 

 lectularia, bed-bug. Nepa cinerea, water-scorpion. Pediculus ca- 

 pitis, head-louse. Phthirius vestimenti ; P. pubis. 



B. COMPLETE METAMORPHOSIS. 



Order 5. Neuroptera. Biting mouth-parts, free prothorax, and two 

 pairs of similar membranous netted wings. Hemerobius perla, lace- 

 fly. Myrmeleon formicarius, ant-lion. 



Order 6. Trichoptera (Phryganidae). Wings covered with hairs and 

 scales ; the larvae aquatic, in tubular cases. Phryganea, caddis-fly. 



Order 7. Strepsiptera. Parasites, with rudimentary mouth-parts, the 

 front wings of the male rudimentary and twisted, the female wingless 

 and vermiform. Xenos vesparum. Stylops mellitse. 



