rrelated with the presence of wings is the wonderful differentiation
of the crust, especially of the thorax, where each segment consists of a
number of distinct pieces; while in the spiders and Myriopods the
segments are as simple as in the abdominal segments of the winged
insect. It is not difficult here to trace a series leading up from the
Poduras, in which the segments are like those of spiders, to the
wonderful complexity of the parts in the thoracic segments of the
Lepidoptera and Hymenoptera.

In his remarks "On the Origin of Insects,"[27] Sir John Lubbock says, "I
feel great difficulty in conceiving by what natural process an insect
with a suctorial mouth like that of a gnat or butterfly could be
developed from a powerfully mandibulate type like the Orthoptera, or
even from the Neuroptera." Is it not more difficult to account for the
origin of the mouth-parts at all? They are developed as tubercles or
folds in the tegument, and are homologous with the legs. Figure 186
shows that the two sorts of limbs are at one time identical in form and
relative position. The thought suggests itself that these long, soft,
finger-like appendages may have been derived from the tentacles of the
higher worms, but the grounds for this opinion are uncertain. At any
rate, the earliest form of limb must have been that of a soft tubercle
armed with one, or two, or many terminal claws, as seen in aquatic
larvae, such as Chironomus (Fig. 202), Ephydra (Fig. 203 _a_, _b_, _c_,
pupa) and many others. As the Protoleptus assumed a terrestrial life and
needed to walk, the rudimentary feet would tend to elongate, and in
consequence need the presence of chitine to harden the integument, until
the habit of walking becoming fixed, the necessity of a jointed
structure arose. After this the different needs of the offspring of such
an insect, with their different modes of taking food, vegetable or
animal, would induce the diverse forms of simple, or raptorial, or
leaping or digging limbs. A peculiar use of the anterior members, as
seen in grasping the food and conveying it to the mouth (perhaps
originally a simple orifice with soft lips, as in Peripatus), would tend
to cause such limbs to be grouped together, to concentrate around the
mouth-opening, and to be directed constantly forwards. With use, as in
the case of legs, these originally soft mouth-feet would gradually
harden at the extremities, until serviceable in biting, when they would
become j