PARTS OP IKSECTS. 
37 
tliei* 1 10n t0 t ^ ese P arts > l ater writers have in many instances regarded 
Moie closely; and in the further progress of the science these 
1 E* JC con sulted with still greater advantage, 
are h' TI - A ’ ° r ^ r,,i g--c«s£.'S, appertain to tlie coleopterous order. These 
mr ' ° 10 num!)er > °f 11 substance resembling leather; for the most 
of , | m °r eable > and Opening by a longitudinal suture along the middle 
'vi 1 i Jac ^' These wing-cases or sheaths are often confounded 
". 1 1 le wings; but they are really not wings from their structure or 
* u lsta ncc,nor do tlicy answer the purpose of flight; they merely open 
0 afford tlie true w ing, concealed beneath, the power of expansion and 
'notion, and close down upon the wing when the insect is at rest, to 
preserve it from injury. Some Coleaptcrn have the elytra united. 
Hie superior surface of the elytra is more or less convex, and the 
lower surface correspondent^ concave: the texture in some, as in 
many ot the Curculimcs and Cerambyces. , is so hard that it is pierced 
w ith difficulty by means of a strong pin ; in others so flexible that they 
spring into their proper form immediately after being bent double. 
J he proportions ol the elytra compared with the body are various; 
1 leir form dissimilar; and the diversity of their surface — arising from 
' " ra 'scd or depressed, protuberances, flu tings, colours, and other cir- 
cumstances— endless. These differences in the elytra furnish some ex- 
cc generic distinctions, and are still more extensively useful in 
constituting the characters of species. 
H alteres, Poisers, or balancers : appendages peculiar to insects of the 
dipterous order, and which, with sufficient reason, are deemed an essen- 
tial character ot that group. These poisers are two short, moveable 
clavated filaments, placed one contiguous to the origin of each wine 
they seldom exceed one-tenth the length of the wing, though in cer- 
tain genera they are rather longer. The capital, or head, in which the 
mament terminates, is either roundish, oval, truncated at the end, or 
compre Sse d at t h e sides : in some insects its situation is directly under 
flimv scale, which also var ies in size and form; and in 
. ' al humlies is apparently wanting. 
not Z CXa >. t J ,ur P 0Be t0 which nature lias destined these organs has 
most n” i hert ° a3CCrtained . iu a 'very satisfactory manner. Tlie 
°pinio! rC ' a ent> an< * P eldla P s * n son ‘e measure tlie most consistent, 
°t‘ the *,. eem ^ f ° ^ e > that they balance or counterpoise with the action 
dancers' 111 ”.*’ ' 6n tne ’ nsect * s U) ®§ht, in tiie same manner as rope- 
ness of 5* c . rci ?® a P°^ c to preserve their equilibrium. The dimimitive- 
these as the** Z* ' S a ,P* a usible objection to this idea. Others consider 
in flio-ht- th°, r ” anS0 ^ 'hat vibratory sound vvhicli dipterous insects emit 
the balancer m?^ Pare *e filmy scale to a kind of tambour, and liken 
conceive dr »m-stick, which striking repeatedly upon it, they 
emit in flight „ , cas]on thls nolse - ],: ls apprehended the sound they 
° 4 cann ot be traced to tins cause; for the best of all possible 
