22 
BRITISH APHIDES. 
Altlioiigh these entrances to the air-passages were 
noticed by Bonnet, they singularly escaped the sharp 
observation of Leon Dufour. 
The pits or depressions formed by the connedivum 
were considered by Hausmann of suflS.cient importance 
to be included in his specific characters. The young 
forms of some species doubtless show these pits very 
markedly, but as they vary by age, and even after- 
wards entirely disappear, I have followed Kaltenbach’s 
example in regarding them as of minor import. 
THE CORNICLES, NECTARIES, OR SIPHUNCLES. 
Considerable diversity, both in form and size, is 
shown by these remarkable and unique adjuncts to the 
sixth abdominal ring. 
In genera like Siphonophora and Drepanosiphum they 
have considerable bulk, and occasionally attain to the 
length of half the insect. As their shape, relative 
length, and colour are very generally constant in the 
adult insect, they are of much consequence in the 
diagnosis of species. 
These cornicles or siphuncles are of a horny nature, 
and constitute the sheaths of certain excretory ducts, 
the delicate walls of which are often seen to traverse 
their interior. They rise above the surface of the 
back into more or less long, moveable, and erect 
tubes. They occur either straight, curved, skittle- 
shaped, or vasiform. Their mouths are often ex- 
panded into trumpet- shaped orifices, which appear to 
have 'a membrane capable of being compressed within 
the aperture, at will of the Aphis, The nectaries are 
very small in some genera, and are entirely wanting in 
others. Thus, in Lachnus these organs are mere per- 
forated tubercles, whilst in Fhyllowera and Trama they 
are obsolete.^ 
Many have been the surmises as to the special 
For these details vide Plates A, B, and 0. 
