THE CATERPILLAR AND THE MOTH
upper wall of the structure is ordinarily collapsed into the cavity of the bulb, but it is capable of being lifted by strong muscles inserted upon it from the walls of the head. The alternate opening and closing of the bulb sucks the liquid food up through the tube of the proboscis and forces it back into the gullet. The moths and butterflies are thus sucking insects, as are the aphids and cicadas, but they are not provided with piercing organs, though some species have a rasp at the end of the proboscis which is said to enable them to obtain juices from soft-skinned fruits.
With the tent caterpillar, it is interesting to note, the maxillae are much longer in the pupa (Fig. 159 I, Mx) than they are in either the caterpillar or the adult moth (Fig. 162, Mx), as if nature had intended the tent caterpillar moth to have a proboscis like that of other moths, but had then changed her mind. The real meaning of this is that the moths of the present-day tent caterpillars are descended from ancestors that had a functional proboscis in the adult stage like that of other moths, and that the reduction of the proboscis of the modern moths has taken place in times so recent that the organ has not yet been suppressed to the same degree in the pupa.
The alimentary tract of the tent caterpillar moth is very different from that of the caterpillar. In the caterpillar, the organ consists of three principal parts (Fig. 164 A), the first comprising the oesophagus (Oe) and the crop (Cr), the second being the stomach, or ventriculus (Vent), and the third the intestine (Int). In an adult moth that is almost mature, but which is still inside the pupal shell (B), the oesophagus has become a long narrow tube (Oe) at the rear end of which the crop forms a small sac (Cr) projecting upward, which may contain a bubble of gas. The stomach has contracted to a pear-shaped bag with very thin transparent walls, and is usually filled with a dark-brown liquid. The intestine has changed radically in form, for it now consists of a long, slender,
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