24 
BEITISH APHIDES. 
held by Kaltenbach,^ who thinks that probably these 
organs are connected with the breathing apparatus, 
which opens from the stomata, and that they assist in 
the more complete aeration of the nourishing fluids. 
The erect position of the cornicles, and the habit 
shown by some species of slowly vibrating them, con- 
firms, he thinks, this view. 
Still the question may be asked. Why are some 
genera of Aphides specially provided with these 
organs, whilst others are wholly devoid of them ? 
Kaltenbach attempts to meet this objection in a 
manner which, if I rightly understand him, may be 
summarised thus. Starting from the position that 
active life-functions in the individual always stand in 
close relation to rapid respiration, he says — 
Those Aphides which, like the genus Si^liono^hora, 
have several broods in the year, and those very 
numerous as to individuals, require the greatest 
amount of oxygenation of their nutritive fluid. Ac- 
cordingly, their stomata are supplemented by long 
cornicles, which effect that change through their 
expanded mouths. This aeration, however, acts un- 
favourably on the life duration of these insects, for he 
has observed that such apterous forms rarely live 
beyond eight days, and that the winged insects have 
an existence not much extended beyond this limit. 
On the other hand, it is to be noted that where, 
as in Lachnus^ these organs are only represented by 
mere tubercles, the brood is restricted solely to one. 
The insect rarely changes its feeding ground, and 
sometimes it may be observed fixed in one spot for 
three months together. 
Again he remarks, that some of the underground 
feeders, and those which hybernate in the crevices of 
bark, are entirely without cornicles, which circum- 
stance, he thinks, is in accordance with their sluggish 
and inactive habits. 
Notwithstanding the ingenuity of this explanation, 
* Kaltenbacli, “ Monograpbie,” ‘ Einleitung/ p. xv. 
