16 
BRITISH APHIDES. 
A large plexus, situated in the centre of the head, 
distributes a fasciculus of nerves to the base of each 
compound eye, and also sends forth several distinct 
and separate filaments to the seat of each superposed 
eye. From this separate distribution of nerves, it 
seems probable, that diverse functions belong to each 
variety of eye.^ 
Fritz Muller, of St. Catherine, Brazil, has started 
the question whether ocelli— or at any rate the size 
of the ocelli— are not connected with the nocturnal 
habits of insects. 
Amongst the Hymenoptera he notices the crepuscular 
movements of some of the Apidce, of the Dorylidce, and 
a social wasp, Jpoica^ all of which are largely ocellated. 
The nocturnal habits of Aphis are not marked, yet all 
the winged forms possess stemmata. The rudimen- 
tary eyes of the underground species are compound, 
and do not show the characters of ocelli, as, from 
above, we might expect, if eyesight is of any advan- 
tage to them. 
THE ROSTRUM, PROBOSCIS, OR HAUSTELLUM 
springs from the base of the deeply sulcated and lobed 
clypeus, which last rises strongly in relief from the 
lower portion of the face. As in other Hemiptera, the 
rostrum is an extension of the labium, which is modified 
into a kind of sheath. This sheath is not completely 
perforated, but is deeply channelled on its upper sur- 
4 face, so as to receive three long, and exceedingly fine 
setce or lance-like piercers. This sheath is formed of 
^ three joints or separate members, of which the first 
is much the longest. The second is more dilated than 
the first, and appears to be perforated, not channelled 
like the others — a modification which probably affords 
a better support to the setse when in action. The 
third joint is short, obtusely pointed, and cleft to the 
apex, from which the setse may be often seen to protrude. 
* Vide Plate B, fig. 5. ^ 
