LEPIDOPTEEA. 167 



from its fetters. It flies away, brilliant and free, and its many- 

 coloured wings glitter in the sun. 



The duration of the pupa state is variable, according to the 

 species and the temperature. Ueaumur placed in a hot-house, 

 in the month of January, some pupae which, in the ordinary 

 course of things, would not have been hatched till the month 

 of May, and a fortnight afterwards the images had appeared. 

 On the other hand, he shut up some pupae in an ice-house during 

 the whole of a summer, and thus retarded their being hatched 

 by a whole year. The influence of the temperature on the period 

 of emerging, and, consequently, the influence of the seasons on 

 the length of this period, are completely brought to light by 

 these experiments.* 



We will now see how the insect delivers itself from the last 

 skin. To quit the pupa case is not so laborious an operation as 

 it was for the same insect to quit the caterpillar's skin. This is 

 because the pupa case is drier ; it does not adhere to every part of 

 the body, but is brittle. Those which are enclosed in a cocoon free 

 themselves of the pupa in the shell itself. So as to witness the last 

 operation which we have to consider, it may be opened, and the 

 pupa drawn out of it with care. If then placed in a box, one sees 

 the metamorphosis take place. To study this last evolution which 

 is now occupying our attention more at his ease, Reaumur covered 

 a large extent of the wall of his study with pupae of the Vanessa 

 polychloros and other species. 



When the parts of the body of the insect have attained to a 

 certain degree of solidity within the envelope, it has no great dif- 

 ficulty in making the thin and friable membrane which surrounds 

 it split in different places. If it even distends itself or moves, a 

 small opening is made in the dried skin. If it reiterates its move- 

 ments, the opening increases in size, and very soon allows the 

 imago to emerge. It is on the middle of the upper part of the 

 thorax that the envelope begins to split. The split extends over 

 the middle of the forehead and back. The pieces of the thorax 

 open, separate themselves from the other parts to which they were 



* They hardly seem from later experiments to be so fully explained. It is a well- 

 known fact that many insects remain in this state a variable time ; the Small Eggar 

 (Bombyx lanestris) sometimes as many as seven years. ED. 



