OBSERVATIONS ON PUPATION.
217
cases he observed the larva digs a hole in the ground more or
less round, open above, wherein, lying on its belly, its back
reflexed in a semicircle, the head and tail elevated to the same
level, it awaits the change into the pupa.3 He gives beautiful
drawings of the pupa, but says nothing about its resting position
in the cell.
If the outer wall of a cell is carefully removed about a week
after it is made, the pupa may be seen with the dorsal side
uppermost lying across the cell, supported only on a number of
short stiff bristles on the interior rim of the thorax and on two
fringed processes at the tail end. The whole of the body is
thus kept away from contact with the surrounding earth except
at the two supporting areas at opposite extremities of the
body. If disturbed, however, the pupa gives a wriggle, causing
it to fall over on its back, but very soon another wriggle raises
it again into its normal resting position. The empty larval
skin is pressed flat against the wall of the cell, where the pupa
cannot come into contact with it.
Pupae observed remained from two to three weeks before
the emergence of the beetle, the eyes, the legs and parts of the
terminal segments of the abdomen becoming dark. The thorax
and elytra of the imago are soft and quite white or cream-
coloured at first, but in twenty-four hours they have almost
reached their normal colouration.
The insect finally escapes through a comparatively small
opening made in the exterior wall towards the top of the cell
above the part of the wall made by the earth removed from
the interior of the cavity.4
HYDROUS.
Some time ago I discovered a larva of H. piceus in a ditch
near Eastbourne. It was swimming slowly along, and was
easily captured and was apparently full fed. I gave it a choice
of going into a bank after the manner of Dytiscus or of making a
hole from the surface of the earth, but it did nothing but wander
about continuously for some days.
In desperation I made a hole in the side of the vertical bank
and induced the larva to enter. The opening was then blocked
3 My observations do not agree with this description; my larva rested on its back, with
head and tail curved together over the ventral surface.
4 Proc. Ent. Soc, 1917, lxxiii.