Page:Insects - Their Ways and Means of Living.djvu/344

 4L), the first four pairs being on the third, fourth, fifth and sixth segments, and the last on the tenth segment. The region of the three segrnents in the caterpillar bear- ing the jointed legs corresponds with the thorax of an adult insect (Fig. 63, Th), and that following corresponds with the abdomen (db). The thorax of the adult insect constitutes the locornotor center of the body, but the worrnlike caterpillar has no special locornotor region, and hence its body is not separated into thorax and abdomen. The thoracic legs of the caterpillar terrninate each in a single claw, but the foot of each of the abdorninal legs has a broad sole provided with a series or circlet of claws and with a central vacuum cup. The abdorninal legs of the caterpillar, therefore, are important organs of pro- gression, and are the chier organs of grasping or of cling- ing to hard or fiat surfaces. The jaws of the caterpillar consist of a pair of large, strong rnandibles (Fig. 152, 3fd) concealed, when closed, behind the labrurn. Each jaw is hinged to the lower edge of the cranium at the side of the rnouth by two ball- and-socket hinges in such a rnanner that, when in action, it swings outward and inward on a lengthwise axis. The cutting edges are provided with a number of strong teeth (Fig. 53), the points of which come together or slide past each other when the jaws are closed. The large complex organ that projects behind or below the rnouth like a thick under lip (Fig. 5 OE C) is a com- bination of three parts that are separate in other insects. These are the second pair of soif jaw appendages, called maxillae (B, C, Mx), and the true under lip, or labium (Lb). The most important part of this cornposite struc- ture in the caterpillar, however, is a hollow spine (A, B, C, Spt) pointed downward and backward from the end of the labiurn. This is the spinneret. Frorn it issues the silk thread with which the caterpillar weaves its tent and its cocoon.

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