ANTENNA 



987 



down to a level, or, the margin remaining entire, the central por- 

 tion must be thrown into plaits, so that its corneules overlap one 

 another. As the latter condition interferes with the examination 

 of the structure much more than the former does, it should be 

 avoided by making a number of slits in the margin of the convex 

 membrane before it is flattened out. Vertical sections, adapted to 

 demonstrate the structure of the ocelli and their relations to the 

 optic nerve, can be only made when the insect is fresh or has been 

 preserved in strong spirit. Mr. Lowne recommends that the head 

 should be hardened in a 2 per cent, solution of chromic acid, and 

 then imbedded in cacao butter ; the sections must be cut very thin, 

 and should be mounted in Canadh, balsam. The following are some 

 of the insects whose eyes are best adapted for microscopic pre- 

 parations ; Coleoptera, Cicindela, Dytiscus, Melolontha (cockchafer), 

 Lucanus (stag-beetle) ; Orthoptera, Acheta (house arid field crickets), 

 Locusta ; Hemiptera, Notonecta (boat-fly) ; JVe-uroptera, Libellula 

 (dragon-fly), Agrion ; Hymenoptera, Vespida? (wasps) and Apidse 

 (bees) of all kinds ; Lepidoptera, Vanessa (various species of), Sphinx 

 ligustri (priA'et hawk-moth), Bombyx (silkworm moth and its allies) ; 

 Diptera, Tabanus (gad-fly), Asilus, Eristalis (drone-fly), Tipula (crane- 

 fly), Musca (house-fly), and 

 many others. 



The antenncv, which are 

 the two jointed appendages 

 arising from the upper part 

 of the head of insects (fig. 

 731, b 6), present a most 

 wonderful variety of confor- 

 mation in the several tribes 

 of insects, often differing 

 considerably in the several 

 species of one genus, and 

 even in the two sexes of the 

 same species. Hence the 

 characters which they afford 

 are extremely useful in classi- 

 fication, especially since their 

 structure must almost neces- 

 sarily be in some way related 

 to the habits and general 

 economy of the creatures to 

 which they belong, although 

 our imperfect acquaintance 

 with their function may pre- 

 vent us from clearly discerning this relation. Thus among the 

 Coleoptera we find one large family, including the glow-worm, fire- 

 fly, skip-jack, <fcc., distinguished by the toothed or seriated form of 

 the antenna?, and hence called Serricornia ; in another, of which the 

 burying-beetle is the type, the antenna? are terminated by a club- 

 shaped enlargement, so that these beetles are termed Clavicornia ; 

 in another, again, of which the Hydrophilus, or large water-beetle, 



FIG. 736. Antenna of Melolontha 

 (cockchafer). 



