2O4 Marsh. 



forming the thorax, the last eleven the abdomen. On the 

 sides of the first thoracic and the first eight abdominal 

 segments are to be seen a couple of small transverse slits or 

 openings. These are the spiracles, and lead into little air- 

 chambers, from which tiny air-tubes spread all over the 

 body, and convey the air necessary to purify the blood. 

 Each thoracic segment bears a pair of legs, but, though 

 these are the true legs, the caterpillar, as you see, does not 

 use them for walking, but only to steady its food when 

 eating, and you notice that each leg is provided with a 

 short, dark hook. The skin on the under side of the third, 

 fourth, fifth, sixth and last segments of the abdomen is 

 extended downwards, forming projections called pro-legs or 

 claspers, and although these are not true legs, it is by means 

 of them that the caterpillar walks ; hence they are some- 

 times termed false legs ; we notice that to make them more 

 effective they are composed of joints, and that these are 

 partly retractile, the one into the other. Try to pull the 

 caterpillar from the twig on which it rests, and you will not 

 find it an easy matter, for the end joint of these pro-legs is 

 provided with minute but very powerful circles of hooks, 

 with which it clings tenaciously to the twig. 



Touch that caterpillar on the twig with a stick ; it brings 

 its head and thoracic segment up suddenly, and throws them 

 back, at the same time withdrawing its head into the front 

 thoracic segment. At this time, with its bright stripes, its 

 anal horn and thrown-back head, it looks very peculiar, and 

 probably, by assuming such an attitude, prevents many small 

 birds from attacking it. This threatening attitude is, how- 

 ever, shown much better by the Privet Hawk moth, in 

 which it is so marked that this insect and a few close 



