THE CATERPILLAR AND THE MOTH
the press and into the spinneret is seen from the side at D.
The silk liquid is gummy and adheres tightly to whatever it touches, while at the same time it hardens rapidly and becomes a tough, inelastic thread as it is drawn out of the spinneret when the caterpillar swings its head away from the point of attachment.
The mouth of the caterpillar lies between the jaws and the lips. It opens into a short gullet, or oesophagus, which, with the pharynx, constitutes the first part of the alimentary canal (Fig. 154, Phy, Oe). The rest of the canal is a wide tube occupying most of the space within the caterpillar's body and is divided into the crop (Cr), the stomach, or ventriculus (Vent), and the intestine (Int). The crop is a sac for receiving the food and varies in size according to the amount of food it contains (Fig. 156 A, B, Cr). The stomach (Vent) is the largest part of the canal. Its walls are loose and wrinkled when it is empty, or smooth
Fig. 157. Crystals from the Malpighian tubules of the tent caterpillar, which are ejected into the walls of the cocoon
and tense when it is full. The intestine (Int) consists of three divisions, a short part just back of the stomach, a larger middle part, and a saclike end part called the rectum (Rect). Six long tubes (Mal) are wrapped in many coils about the intestine and run forward and back in long loops over the rear hall of the stomach. The three on each side unite into a short basal tube, which opens into the first part of the intestine. The terminal parts of the tubes are coiled inside the muscular coat of the rectum. These tubes are the Malpighian tubules.
When a tent caterpillar goes out to feed, the fore part of its body is soft and flabby; when it returns to the tent the same part is tight and firm. This is because the tent caterpillar carries its dinner home in its crop, digests it
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