18 A BOOK OF INSECTS 



The manner in which the chrysalis becomes attached to 

 the silken pad is rather complex, and not at all easy to 

 observe. The chrysalis appears to grasp the old cater- 

 pillar skin, which still retains its hold on the support, 

 between two of its abdominal segments. It then with- 

 draws its tail, which terminates in a many-hooked process 

 called the cremaster, and thrusts this upwards against the 

 silken pad. The hooks of the cremaster at once become 

 entangled, and the chrysalis deliberately strengthens the 

 hold thus gained by vigorously whirling and twisting its 

 body. Incidentally, the now useless caterpillar skin is 

 dislodged and falls to the ground. At first the chrysalis 

 is elongate and soft, but it rapidly contracts, hardens, and 

 assumes its characteristic form and colouring. Some 

 three weeks later its skin breaks open, and the butterfly 

 emerges, limp and comparatively helpless. 



It is important to realise that the butterfly, when it 

 escapes from the chrysalis, is in every way perfect, with 

 the form and size of maturity, save for the wings and the 

 abdomen. The former are small, pad-like organs, while 

 the latter is swollen with the fluids which will flow into 

 and fill out the wings. This influx of fluids is exceedingly 

 rapid. The wings grow steadily as we watch until 

 they attain their full size. The principle which underlies 

 this marvellous transformation may be described briefly 

 as follows : The expansion of the wings is due directly to 

 blood-pressure — the blood being forced from the body to 

 the wings chiefly by the contractions of the abdominal 

 muscles. In the newly-emerged insect the tw T o mem- 

 branes of which the wing is formed are soft and corrugated, 

 and expansion consists in the flattening out of the folds 

 under pressure of the incoming fluids. We see, therefore, 

 that the wing is virtually a sac, which would tend to 

 expand into a balloon-shaped bag were it not for numerous 



