72 
BEITISH APHIDES. 
The duration of some of our flowering plants and 
annuals is often limited to a few months. Very gene- 
rally we find that the disappearance of the Aphides 
which peculiarly infest such plants is contemporaneous 
with their decay ; indeed, it would seem to be neces- 
sarily so. Yet it is not easy to conceive in what con- 
dition these Aphides exist during the rest of the year. 
There can be no question that some species hibernate, 
and probably retire under the soil to do so, but this is 
by no means the rule. On the other hand, oviposition, 
so far as the Aphidince are concerned, is confined to 
late autumn. Even then the process by no means 
occurs — if it occurs at all — at regular yearly intervals. 
It will appear to be little better than a guess, that the 
spring Aphides oviposit early, and that the ova rest in 
the earth until the return of spring. 
MIGRATION OF APHIDES. 
The addition of wings to the viviparous females 
obviously must much facilitate the spread of each 
species. This modification of form does not occur at 
fixed or stated intervals, but appears to be in some 
measure induced by an overcrowded state of the colony, 
and with a deficiency of food. Grardeners are well 
aware of the sickly and poisoned conditions produced 
in those plants which are subjected to the exhausting 
and irritating attacks of Aphides. When the nutri- 
tive juices of the infested plants begin to fail a change 
commences in the larvse of those Aphides which are 
subsequently born. Swellings occur on the sides of 
the meso- and the meta-thorax, within which the wings 
of the future imago are developed. These altered 
forms constitute the pupse, which often show consider- 
able differences both in markings and colour from the 
other metamorphic stages. It is to be remarked that, 
although numerous embryos may be seen in a consi- 
derably matured condition within their coverings. 
