12 CATERPILLARS AND THEIR MOTHS 



crawl. Young caterpillars ofteu spin single threads to 

 guide tliem back to a starting-point or to drop from a 

 twig without injury. 



The thoracic segments of the body have the six true 

 legs, two on each segment. The first segment often 

 has a horny plate across the top, or a crest of points 

 or'tubercles, and the second and third segments some- 

 times have tubercles or marks which are more con- 

 spicuous than those of the abdominal segments. The 

 second and third segments have no spiracles. 



The third, fourth, fifth, and sixth abdominal seg- 

 ments have the props or prolegs with tips, or ijlan'tce^ 

 adapted to clinging to the stems or twigs, and the last 

 segment has the anal props and anal plate or shield, 

 a thick flap which covers the anus or vent. This 

 segment is often called the anal segment. 



The spir'acles, or breathing-holes, are low down on 

 the sides, one pair on each segment, except the second 

 and third. 



The eighth abdominal segment, which is the eleventh 

 segment of the body, often has a horn, tubercle, or 

 other mark more conspicuous than any on the other 

 abdominal segments, and one soon grows used to look- 

 ing for characteristic marks on the first three and 

 eleventh segments. The anal shield often has a 

 mark around its edge or a peculiar arrangement of 

 tubercles. There may be thirteen segments of the 

 body, but the last two are usually so united as to 

 seem one. 



The anal props are very thick and have a very firm 

 grasp. 



The spiracles admit air to the tra'cJiece, or air-tubes, in 



