52 INJURIOUS AND USEFUL INSECTS 



is accordingly reckoned in books as nine. Of these the first 

 two bear no appendages, the third, fourth, fifth and sixth bear 

 each a pair of feet known as prolegs, which are different in 

 form from the thoracic legs, and are not succeeded by legs 

 in the pupa or imago. The remaining segments bear no 

 appendages till we come to the last of all, which carries a pair 

 of unusually large anal feet. Deviations from this arrange- 

 ment are not uncommon. The last pair of abdominal legs 

 may cease to act as feet, and become transformed into a pair 

 of protrusible filaments, as in the larva of the puss-moth and 

 some others. Two or three of the fore pairs of abdominal 

 legs disappear or become shorter than the rest in some larvae, 

 while in the numerous family of geometers, only the legs of 

 the sixth abdominal segment and the anal feet remain. These 

 larvae are distinguished by their peculiar looping movements, 

 and by their habit of extending the body in a straight line 

 from the twig to which they attach themselves, which they 

 often resemble so closely that they completely escape observa- 

 tion. The abdominal feet of a caterpillar are usually short, 

 and end in a double crown of hooks. The eight fore- 

 most abdominal segments bear spiracles, and these are often 

 very conspicuous, being unlike in colour to the surrounding 

 skin. The anus opens on the last segment, and is usually 

 concealed by a triangular valve. 



When these points have been observed, and also the 

 characters peculiar to the particular species under observation, 

 the caterpillar should be opened along the back with a pair 

 of fine scissors. The skin must be carefully separated from 

 the underlying parts, and laid out with pins on each side. A 

 shallow dissecting dish lined with paraffin or cork* should be 

 used, and when the skin has been reflected and secured, water 

 enough to cover the insect should be added. The muscles of 

 the body-wall and the heart need not be separated from the 

 skin.f The head should be secured by two crossed pins, but 

 not injured in any way. 



* A small tin tray, such as pastrycooks use, nialtes a capital dissecting 

 tray for insects. Mix hot paraffin wax and asphalt, and pour o little on 

 the bottom. 



t To make a satisfactory dissection of the heart it must first be hardened 

 with suitable reagents, then removed from the body, together with the 

 uninjured dorsal integument, and last of all dissected away from the 

 adjacent parts. Beginners are not recommended to attempt this. 



