56 INJURIOUS AND USEFUL INSECTS 



operation is not perfectly effected at first, repeat it. Some 

 people use a ruler instead of the thumb, but this is a rougher 

 method, and more liable to injure the skin. 



The skin, when successfully emptied, is flat and much 

 contracted. The muscles of the body-wall are still in place, 

 and cause shrinking of the skin. A glass-pipe of suitable 

 size passed into the anus might now be used as a blow-pipe 

 to inflate the skin, but some special arrangements are necessary 

 to prevent the skin from collapsing as soon as the pipe is 

 removed. Various methods have been proposed, but nothing 

 answers better than the following : — Take a glass pipe, drawn 

 out at one end to a moderately fine point. To this fasten 

 two pieces of watch-spring in the following way. Cut the 

 watch-spring by striking it with a steel point and a hammer. 

 This will give a notched edge on each side of the fracture, 

 and such edges are excellent for holding. The spring must 

 further be softened by heating in a flame and slow cooling, 

 so that it will take any required position. Then arch both 

 upper and lower springs in opposite directions and tie them 

 into the required position with thread. The free ends of the 

 springs must press against the glass pipe, and one must be 

 longer than the other by about a quarter of an inch. The 

 springs should not be attached directly to the glass tube, 

 but to an outer tube which slides easily upon it. A split 

 metal tube of suitable size to slide upon the glass tube can be 

 got from a penholder or some kinds of pocket-pencil. 



When all is ready draw the sliding tube away from the 

 point of the glass tube, insert the tip of the glass tube into 

 the anus, then, holding the springs apart, slide the split 

 tube forwards. Bring the end of the longer spring, which 

 is to be held downwards, against the under side of the larva, 

 just in front of the anal feet, while the shorter spring is made 

 to hold the skin of the dorsal surface. The larva hangs 

 down quite limp, but stands out straight when air is forced 

 into it by the pipe. See whether the air escapes too rapidly, 

 and if any considerable leak is discovered, readjust the 

 springs. 



Air-pressure may be got by blowing with the mouth, by a 

 hand-syringe, or even by the gentle contraction of an india- 

 rubber toy balloon. A wire clip on an india-rubber connection 

 will prevent the escape of the air when the skin is inflated. 



