tuated behind the simple eyes, or ocelli; these are deciduous organs,
apparently aiding the insect in moving about its cell. They disappear in
the mature pupa.

[Illustration: Fig. 29. Fig. 30. Fig. 31.

Fig. 31. Larva of Halictus parallelus.

Fig. 29. Larva of Andrena vicina.

Fig. 30. Pupa of Halictus parallelus seen from beneath.]

To those accustomed to rearing butterflies, and seeing the chrysalis at
once assuming its perfected shape, after the caterpillar skin is thrown
off, it may seem strange to hear one speak of a "half-pupa," and of
stages intermediate between the larva and pupa. But the external changes
of form, though rapidly passed through, consisting apparently of a mere
sloughing off of the outer skin, are yet preceded by slow and very
gradual alterations of tissues, resulting from the growth of cells. An
inner layer of the larva-skin separates from the outer, and, by changes
in the form of the muscles, is drawn into different positions, such as
is assumed by the pupa, which thus lies concealed beneath the
larva-skin. But a slight alteration is made in the general form of the
larva, consisting mostly of an enlargement of the thoracic segments,
which is often overlooked, even by the special student, though of great
interest to the philosophic naturalist.

From Mr. Emerton's observations we should judge that the pupa state
lasted from three to four weeks, as the larvae began to transform the
first of August, and appeared during the last week of the same month as
perfect bees.

The Andrena is seen as late as the first week in September, and again
early in April, about the flowers of the willow. It is one of the
largest of its genus and a common species.

Having, in a very fragmentary way, sketched the life history of our
Andrena and had some glimpses of its subterranean life, let us now
compare with it another genus of solitary bee (Halictus), quite closely
allied in all respects, though a little lower in the scale.

The Halictus parallelus excavates cells almost exactly like those of
Andrena; but since the bee is smaller, the holes are smaller, though as
deep. Mr. Emerton found one nest in a path a foot in depth. Another
nest, discovered September 9th, was about six inches deep. The cells are
in form like those of Andrena, and like them, are glazed within. The egg
is rather slenderer and much curved; in form it is long, cylindrical,
obtuse at one end, and much smaller at the other. The larva (Fig.