296 TRANSFORMATIONS OF INSECTS. 
in contact with the respiratory orifices. The beetle is equally 
interesting when it is about to lay its eggs, and whilst it is forming 
its cocoon. Crawling over the aquatic plants head downwards, it 
lays its eggs and immediately drags its silk-drawers over and 
around them, and it envelopes them in a cocoon, which it fixes 
either to a leaf or to a stem. But sometimes the cocoon floats 
by itself. These cocoons are of a light grey colour, are a short 
oval in shape, and have a long conical pedicle. 
The beetle on the leaf close to the surface of the water, in 
the engraving on the previous page, is laying its eggs and forming 
its cocoon. Another beetle is on the ground on the left hand ; 
a nymph is enclosed in its cell on the right, and above it there is 
a full-grown larva. 
As soon as the young larve are hatched they begin.to feed, 
EGG COCOONS OF Aydrophilus piceus. (Magnified.) 
and grow very rapidly; and when they have attained their full 
size they are large insects of a dark grey colour, and the hard 
parts of the head and of the thorax are of a lustrous brown tint. 
Whilst they are quiet, and even during their progression, the head 
and the tail are turned up so that the body is always more or less 
curved. They swim easily with the assistance of ciliated legs and 
a flexible abdomen. The nymph has some very strong and thick 
hairs on the thorax and abdomen, but their use is unknown. 
The central cocoon represented in the above engraving is 
attached to a leaf, but that on the left hand is isolated. On the 
right hand a cocoon has been opened so as to show the position 
of the eggs in it. 
The Dytiscide live in most stagnant waters, and in the little 
streams which roll slowly along on account of their water weed. 
These beetles are provided with large wings, with which they can 
