EXTERNAL ANATOMY OF INSECTS. 515 
the joints of the antennz are often armed at their apex 
with spines, sometimes on the upper side and sometimes 
below. In some aquatic beetles.(Gyrinus, Parnus) these 
organs are furnished with an auricle at their base, which, 
like the lid of a box, shuts them in when unemployed, 
and protects them from the water *. 
The portions into which antennz may in general be 
considered as divided, have been sufficiently explained 
to you above; but it may not be amiss to add here a few 
words on the principal variations in their structure that 
I have had an opportunity of observing. The scapus> 
or first joint, which includes the dulbus, is usually the 
most conspicuous joint in the antenna (exclusive, I mean, 
of the capitulum, in those in which that organ terminates 
in a knob), it being thicker and often longer than the suc- 
ceeding ones. In the Capricorn and Darkling beetles, 
indeed (Longicornia and Melasoma), the third joint is the 
longest, but the scape is still the thickest; and in the 
stag-beetles (ucanus), many of the weevil tribes (Rhynco- 
phora), and those of the bees (Mellifera), except in the 
males, it is as long nearly as the remainder of the an- 
tenna, which forms an angle with it. In shape it is 
generally somewhat curved and subclavate, or increasing 
in size from the base to the summit; but it is sometimes 
straight and filiform, at others oblong or square, at 
others again triangular, in several instances three-sided : 
in one (Genuchus cruentus °) it is, as it were, broken, the 
upper part forming nearly a right angle with the lower ; 
in Cerocoma Schefferi it is foliaceous; and it is occasion- 
ally suborbicular: and probably many other forms might 
be enumerated. 
@ Prares XII. Fic. 29; and XXV. Fie. 28. a. 
» Prates XI. XU. XXYV. kk’. °* Linn. Trans. xiv. 569—. 
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