GENERAL NOTES ON INSECTS. 341 
It was a step of some importance in morphology when Savigny 
showed that the three pairs of anpendages about the mouth are 
homologous with the other appendages, z.¢. are masticatory legs. 
(1) Farthest forward lie two mandzb/es, the biting and cutting jaws. 
These are single-jointed, and thus differ from the organs of the same 
name in the crayfish, which bear a three-jointed palp in addition to the 
hard basal part. In those insects which suck and do not bite, e.g. 
adult butterflies, the mandibles are reduced. 
(2) Next in order is the first pazr of maxdllg. Each maxilla consists 
of a basal piece (protopodite), an inner fork (endopodite), and an outer 
fork (exopodite). The entomologists divide the protopodite into a 
lower joint, the cavdo, and an upper, the s¢zZes ; the endopodite into an 
internal Jacézza and an external galea; while the exopodite is called 
the maxzllary palp. 
(3) The last pair of oral appendages or second maxille are partially 
fused, and form what is called the /adcum. The lower and upper 
joints of their fused protopodites are called sadmentum and mentum ; 
the endopodites on each side are double, as in the first maxille, and 
consist of internal /acénza and external Zaraglossa ; the exopodites are 
called the labzal palps. 
The three pairs of thoracic legs consist of many joints, are usually 
clawed and hairy at their tips, and differ greatly according to their uses, 
as may be seen by comparing, for instance, the hairy feet by aid of 
which the fly runs up the smooth window-pane, the muscular limbs of 
grasshoppers, the lank length of those which characterise ‘‘ daddy-long- 
legs,” the bees’ legs with their pollen baskets, the oars of water-beetles. 
Wings.—These arise as flattened hollow sacs, which grow 
out from the two posterior segments of the thorax. They are 
moved by muscles, and traversed by “ veins” or ‘‘ nervures,” 
which include air-tubes, nerves, and vessel-like continuations 
of the body cavity. Most insects have two pairs, but many 
sluggish females and parasites, like lice and fleas, have lost 
them. On the other hand, there is no reason to believe 
that the very simplest wingless insects, known as Collembola 
and Thysanura, ever had wings. 
There are many interesting differences in regard to wings in the 
various orders of Insects. Thus in beetles the front pair form wing- 
covers or elytra; in the little bee parasites—Strepsiptera—they are 
twisted rudiments ; in flies the posterior pair are small knobbed stalks 
(halteres or balancers); in bees the wings on each side are hooked 
together. When the insect is at rest, the wings are usually folded neatly 
on the back ; but dragon-flies and others keep them expanded ; butter- 
flies raise them like a single sail on the back; moths keep them flat. 
Many wings bear small scales or hairs, and are often brightly coloured. 
It is well known that the colours also vary with sex, climate, and 
surroundings. Most interesting are those cases in which the colours of 
an insect harmonise exactly with those of its habitat, or make it a 
mimetic copy of some more successfully protected neighbour. 
