HEAD AND ADJUNCTS. 
13 
criminating characters. In Siphonophora and like 
genera the seventh and last joint is very long, and 
often imbricated. 
In the Lachninee, the seventh joint, although objicms, 
is much curtailed in length, and here it shows the^rst | 
tendency to abo rt. In the Chermesinse this joint so 
far disappears that it is represented by a mere nail or 
wart-like appendage ; and, as this last portion shows no 
articulation, it has been ignored by Kaltenbach and 
others, who regard this genus as possessing five 
joints only. To the question whether or not this 
appendage is to be regarded as a little joint, must be 
referred the different diagnoses of identical genera, as 
given by Koch, Passerini, and others. The first and 
second joints of the antennae in the whole family of 
Aphides are shorter, rounder, and thicker than those j 
which follow. The first is either articulated directly 
to the head, or else, as before stated, it is placed on 
the frontal tubercle. The third joint is almost always 
the longest, and has often peculiar characters attached 
to it. Thus the alate males and viviparious winged 
females often show it plentifully studded with circular, 
or irregular, hollow tubercles, the outer rims of which 
appear to be connected with delicate membranes, 
which are drawn, like those of a drum, over the mouths.* 
If the views of Newport and others are correct in 
ascribing to the antennse some function connected with 
a sense analogous to hearing, it is here suggested, that 
these membranes may vibrate to waves of sound, and f 
probably have an action similar to the membranous 
organs known to exist at the bases of the antennae 
of some Blattidae and Gryllidae. The sense of hear- 
ing has been proved to be acute in both these 
families. 
The winged males of Aphides have longer antennae 
than the winged viviparous and apterous females of the 
same species. Possibly their more active and roving 
* The reader is referred to the first tliree plates, A, B, and 0, for illus- 
trating this and other like details in anatomy. 
V 
