OBSERVATIONS ON PUPATION.
221
their cells when put into similar conditions, and all pupated
without any difficulty, and the beetles emerged successfully.
The earth was kept damp by limiting the escape of moisture
and by occasional slight spraying with water.
In some cases the roof of the cell was formed to a greater
or lesser extent by the glass cover, thus exhibiting the pupa
inside, in others it was half an inch or even more below the surface.
As an illustration of Miger's style I cannot do better than
quote his graphic description of the conclusion of the meta-
morphosis, which I was able to observe and generally confirm.
He says: "The pupal state lasted for three weeks, during
"which all the chitinous parts gradually became coloured. The
"final metamorphosis took place in the following manner: A
"long white envelope split down the back of the pupa which
"had already developed into the perfect insect; the Hydro-
"philus turned on its back, and with the help of its feet and
"some undulatory movement of its segments it succeeded in
"getting completely rid of the skin. The elytra which had
"rested on the belly were immediately placed on the back;
"the wings unfolded and remained extended until they had
"become firm; soon the insect, withdrawing them under its
"elytra, which were still white and without consistency, raised
"itself without effort and placed itself on its legs, which were
"only slightly hardened. It attained in twenty-four hours its
"usual brown colour, and rested twelve days in the earth without
"making any movement. At the end of this time it began to
"be agitated and the firmness of its feet and its mandibles then
"enabling it to force its prison, it escaped through a rather small
"opening by means of the flexibility of its elytra and the com-
"pressibility of its body."
Note.—A very complete account by Hans Blunck of the
metamorphoses of Dytiscus marginalis appears in the Zeits.
fur Wissenschaftliche Zoologie (Leipzig) 1914, pp. 76-151 and
1923-4, pp. 171-391, entitled "The Development of Dytiscus
marginalis L. from Egg to Imago." Part 1. The Embryonic
Life. Part 2. Larval and Pupal Life. A very full bibliography
is appended.
As far as I know this has not been translated into English,
nor have the investigations been referred to in any of our text
books on the subject.