LEPIDOPTERA. 199 
cell lying immediately behind vein III is cell III, and that lying 
immediately behind vein V is cell V. 
Accessory Cells. —In many genera the branches of vein III of the 
fore wings anastomose 
so as to form one or 
more cells beyond the 
apex of the discal cells 
(Fig. 239, a.c.) ; these 
are the accessory cells. 
Discal Vein. — The 
cross vein at the outer 
end of the discal cell is 
termed the discal vein 
(Fig. 239, d.v.). 
Patagia. — At the 
base of each fore wing 
there is a scale-like ap¬ 
pendage; these are the 
patagia. The patagia 
are borne by the protho¬ 
rax, and in many cases 
are capable of consider¬ 
able movement. 
In descriptions of 
Lepidoptera reference is 
often made to the palpi. 
These form the double beak-like projection which extends forward 
from the lower surface of the head. In most Lepidoptera only the 
labial palpi are well developed; but in some of the more generalized 
forms the maxillary palpi are also present. 
The presence or absence of ocelli 
is a character which is sometimes of 
considerable importance. These or¬ 
gans are situated, one on each side, 
above the compound eye and near its 
margin (Fig. 240). But it requires some 
skill to find them when they are present, 
on account of the long scales clothing the head. 
The Phylogetiy of the Lepidoptera. —Since the general acceptance 
of the theory of evolution—that is. the theory that the higher animals 
and plants have been developed from lower ones—it has become evi¬ 
dent that the only sure basis for classification is a knowledge of the 
Fig. 
340.—Head of moth, showing 
position of ocellus. 
Fig. 239.—Wings of Notolophus leucostigma. 
