THE PEKFECT INSECT. 



body, and with, its tail, all of which, it employs for rowing, balanc- 

 ing, and guiding itself in the water, the tail playing the part of 

 the rudder. 



41. Such is the mobility of these members, that even when the 

 creature is in repose, all the paddles are in rapid motion ; the 

 steering prong of the tail alone being at rest. 



Independent of its faculty of locomotion by means of its legs, 

 paddles, and tail, it possesses a power of leaping and springing in 

 the water, by bending its body backwards, and then suddenly 

 straightening it ; by this movement it raises itself to the surface 

 with great celerity. 



42. During the second stage of the life of this insect, called the 

 state of chrysalis, it retains the faculty of swimming ; its motions 

 are altogether subservient to its will, and it leaps with great ala- 

 crity. As the epoch, however, approaches at which it is to pass 

 into the third and most perfect state, in which it receives the name 

 of day-fly, some parts of it assume a metallic lustre, just as if 

 the thin casing in which it is wrapped like a mummy, were partly 

 filled with mercury ; this casing is so thin and translucent, that 

 every part of the body of the perfect insect, which is soon about 

 to emerge from it, is plainly enough visible through it. The me- 

 tallic appearance, 'just mentioned, is supposed to arise from the 

 evolution of a small quantity of gas from the body of the insect 

 in the change which it is undergoing ; this gas, by insinuating 

 itself between the case of the chrysalis and the body of the insect, 

 helps to detach the former from the latter, and thus facilitates 

 the natural process by which the insect emerges from its prison. 

 The envelope of the chrysalis is adapted to the form and members 

 of the insect, just as a glove is to the hand, so that after the insect 

 has escaped from it, this envelope will exhibit with great precision 

 its shape and proportion?. 



43. When the creature has divested itself of its envelope, it 

 remains apparently inert for a few minutes on some neighbouring 



Fig. 31. 



plant, where it carefully cleanses its wings, and divests them of 

 the last pellicle of the sheath in which they had been inserted ; 

 it then assumes the beautiful form, and exercises the functions 



79 



