600 ARTHROPODA. 



present, the front pair being larger than the hinder pair. The wings 

 are membranous, with a few distant nervures, which are generally con- 

 nected by cross-veins so as to form large polygonal cells. The females 

 usually with an ovipositor, which maybe converted into a " sting'''' 

 (aculeus). 



As regards their distribution in time, very few fossil forms of the 

 Hymenoptera are known in deposits older than the Tertiary. Of 

 the very limited number of Mesozoic forms one of the most ancient 

 is the PalcEomyrmex prodromus, described by Heer from the Liassic 

 rocks of Switzerland, which belongs to the family of the Ants 

 (Formicidcz), a family which has also representatives in later Jurassic 

 deposits. In the Tertiary rocks the remains of Hymenoptera are 

 more abundant, almost all the existing families of importance being 

 represented ; but none of the fossil forms are of special interest. 



Order V. Strepsiptera. — Females without wings or feet, pa7-a- 

 sitic. Males possessing the posterior pair of wings, which are large, 

 membranous, and folded longitudinally like a fan. The anterior pair 

 of wings rudimentary, represented by a pair of singular twisted organs. 

 Jaws rudimentary. 



The Strepsiptera constitute a small order, which includes certain 

 minute parasites of Bees and other Hymenoptera. The females are 

 grub-like, but the males are winged. A single example of one of 

 the winged males of this singular group of insects has been detected 

 in amber, and has been referred to the extinct genus Tricena. 



Order VI. Coleoptera. — This great order of Insects includes 

 the " Beetles," which are characterised by their strong chitinous 

 integument and the complete adaptation of the mouth-organs for 

 biting, the mandibles being well developed. The anterior wings are 

 useless as organs of flight, and are hardened by chitine, so as to form 

 protective cases {elytra) for the posterior wings, these being membranous, 

 and being folded transversely and longitudinally in repose. The nerv- 

 ures of the hind-wings are few and distant, cross-veins being rai-ely 

 developed. The inner margins of the elytra (fig. 449) are generally 

 straight, and when in contact they forni a longitudinal suture. 



As regards their distribution in time, the oldest types of the 

 Coleoptera, recognised by Mr Scudder, belong to the Curculionidce 

 (Weevils), and appear in the Triassic rocks {Curculionites pro- 

 dromus). The Jurassic rocks have yielded a number of types of 

 this family also ; while Heer describes other forms from the Creta- 

 ceous rocks of Greenland ; and about one hundred species of 

 Weevils, belonging mostly to existing genera, have been mentioned 

 or described from the Tertiary rocks. The great existing families 

 of the ChrysomelidcE, Buprestidce, and Ca?-abidce (fig. 449, b) are 

 also all represented by Triassic forms ; and all have more or less 

 numerous Jurassic and Tertiary representatives. Of the remaining 



