STATES OF INSECTS. (Pupa.) 287 
fixed itself thus perpendicularly, draws first its two an- 
terior legs out of their case, and moves them forward, 
and next the two intermediate ones; then inclining it- 
self towards the water, it rests its legs upon it, for water 
is to them a soil sufficiently firm and solid to support 
them, although surcharged with the weight of the insect’s 
body. As soon as it is thus upon the water, it is in safety ; 
its wings unfold themselves and are dried, and it flies 
away. All this is the work of an instant?. 
The pupeze of Chironomus plumosus proceed from those 
red worm-like larvae so common throughout the summer 
in tubs of rain-water, &c., described by Reaumur ®. 
They are not inclosed in cases, but are of a greater spe- 
cific gravity than the water at the bottom of which they 
reside, until within a few hours of the exclusion of the 
fly. ‘They have the power of swimming, however; and 
by moving the tail alternately backwards and forwards, 
can slowly raise themselves to the top of the water. But 
here occurs a difficulty. For the extrication of the imago 
it is necessary that they should remain quietly suspended 
at the surface; and moreover that the thorax, in which 
the opening for its exit is to be made, should be at least 
level with it: and this is precisely what takes place. If 
you watch one of these pupz when it ascends from the 
bottom, you will see that as soon as it has reached the 
top it remains suspended there motionless; and that its 
thorax is the highest part of the body, and level with 
the surface. Now the question is, in what way this is 
accomplished ? How can a pupa of greater specific 
gravity than water, remain suspended without motion at 
@ Reaum, iv, 610—. 
> Ibid. y. 30—. ¢. v. f. 1—10. See above, p. 153—. 
