i8o ROUND THE YEAR 



again with the finger and thumb of the right hand. 

 Then the right finger must be turned so that the 

 thread rests upon its nail, which answers to the hard 

 and shiny surface of the head of the larva. By this 

 extempore model the reader can better understand 

 how the thread issuing from the mouth is made to 

 sweep across the body in an arc of the requisite size, 

 gliding smoothly all the time over the polished head 

 Each thread as it is fixed is passed backwards over 

 the spiny segments, which contract or dilate for the 

 purpose of aiding its passage, and thus by the addi- 

 tion o many threads the girdle at length acquires 

 due strength. Then the fore part of the body is 

 extended, the head passed well in front of the 

 girdle, and the larva, now provided with a two-fold 

 attachment, can proceed to divest itself of its larval 

 skin without fear of falling to the ground. 



Reaumur tells us next how the Large Cabbage White 

 manages. When pupation approaches the larva makes 

 its web and hillock, as already described, and catches 

 hold with its hooked claspers. The body is smooth, 

 and so flexible that the head can be bent backwards 

 and made to touch the fifth segment. Thus doubled up 

 it spins the girdle from side to side, passing it round 

 the furrow between the fifth and sixth segments of 

 the body. When sufficient silk has been spun, the 

 body is straightened, and comes into the best position 

 for support by the girdle. 



The third method of girdle-spinning is practised -by 

 the Swallow-tail Butterfly. Here the larva* holds on 

 by its tail and abdominal feet, the head is thrown well 

 back, and the thoracic feet are in the air. The thread,. 



