564 INSECTS AND ARACHNID A. 



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

 by making a number of slits in the margin of the convex mem- 

 brane before it is flattened out. Such preparations may be 

 mounted either in liquid, or in Canada balsam ; the latter being 

 preferable when (as sometimes happens) the membrane is so 

 horny as to be but imperfectly transparent. Vertical sections, 

 adapted to demonstrate the structure of the ocelli and their re- 

 lations to the optic nerve, can of course be only made when the 

 body of the insect is fresh ; and these should be mounted in 

 fluid. The following are some of the Insects, whose eyes are 

 best adapted for Microscopic preparations : Coleoptera, Cicindela, 

 Dytiscus, Melolontha (cockchafer), Lucanus (stag-beetle) ; Or- 

 thoptera, Acheta (house and field crickets), Locusta ; Hemiptera, 

 Notonecta (boat-fly) ; Neuroptera, Libellula (dragon-fly), Agrion ; 

 Hymenoptera, Vespidae (wasps) and Apidee (bees) of all kinds ; 

 Lepidoptera^ Vanessa (various species of butterflies), Sphinx 

 ligustri (privet 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. 



385. The Antennce, which are the two jointed appendages 

 arising from the upper part of the head of Insects (Fig. 283, 6, 5), 

 present a most wonderful variety of conformation 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 classification ; especially since their structure must 

 almost necessarily 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 prevents us from 

 clearly discerning this relation), so that their resemblances and 

 differences will generally be found to coincide with those re- 

 semblances and differences in general conformation, on which 

 every " natural" arrangement must be founded. Thus, in the 

 Coleopterous order, we find one large family, including the glow- 

 worm, fire-fly, skip-jack, &c,, distinguished by the toothed 

 or serrated form of the antennae, and hence called Serricornes ; 

 in another, of which the " bury ing-beetle" is the type, the 

 antennae are terminated by a club-shaped enlargement, so that 

 these beetles are termed Olavicornes ; in another, again, of which 

 the Hydrophilus or "large water-beetle" is an example, the 

 antennae are never longer and are commonly shorter than one 

 of the pairs of palpi, whence the name of Palpieornes is given 

 to this group ; in the very large family that includes the Lucani 

 or " stag-beetles," with the Scarabaei of which the " cockchafer" 

 is the commonest example, the antennae terminate in a set of 

 leaf-like appendages, which are sometimes arranged like a fan 

 or the leaves of an open book (Fig. 285), are sometimes parallel 

 to each other like the teeth of a comb, and sometimes fold one 

 over the other, thence giving the name of Lamellicornes ; whilst 

 another large family is distinguished by the appellation Longi- 



