?(42)
reasons for this attitude, namely, (1) Anopheline larvæ do not possess the
characteristic external air-tube already mentioned, and (2) on the upper surface
of the abdominal segments of Anopheline larvæ there are little cup-shaped
structures called palmate hairs which open at the surface of the water and,
acting like floats, keep the body of the larva in contact with the surface.
These palmate hairs can be easily seen by examining an Anopheline larvæ in a
drop of water under a low power of the microscope; they are not present in
the larvæ of any other kind of mosquito and together with the absence of the
external air-tube render it easy to recognise such larvæ. (Plate IV, d.)
How to collect larvœ and breed them out.-When going out to collect larvæ
it is best to take a large tin mug with a handle and some wide-mouthed
bottles. As Anopheline larvæ are often difficult to see, we should not leave
any pool or stream because we cannot see larvæ in it, but should stoop down
at the edge of the water and scoop the tin quickly through it under the grass
at the edge, bringing it out full of water. Then, if the tin is allowed to
stand on the ground for a few moments, any larvæ that have been dipped up
in it will rise to the surface and be easily recognised. By fishing in this way
at the edges of several parts of a pool or stream we shall either catch a good
many larvæ, or make certain that the pool or stream is free from them.
If any are caught they should be transferred with some of the water into
one of the wide-mouthed bottles, keeping the larvæ from different pools in
different bottles. The mouths of the bottles should be covered with a
piece of coarse muslin, and after a few days the larvæ will develop into
pupæ and then into adult mosquitoes, which can be transferred to another
bottle, killed, and mounted for examination. In this way we shall learn
after a time exactly what species of mosquitoes are found in the different
breeding places.
The pupœ of
mosquitoes.
(3) The pupœ are small comma-shaped creatures bearing no resemblance
to the larvæ, and they breathe by means of two trumpet-shaped projections
attached to the head, so that they lie with their heads at the surface and
their tails downwards. It is not always easy to distinguish the pupæ of
Anopheline from those of other kinds of mosquitoes, but as the matter is not
of much importance we need not consider it here. A drawing of an
Anopheline pupa is given in Plate IV, e.