bat little practical value to the farmer or horticulturalist, the fact of 
the rapid multiplication of these insects being the chief point in 
connection with their reproduction with which he is concerned. 
As before intimated one part of the life history of these insects, 
to-wit: the method by which they pass the winter—does not appear to 
be well understood. That a number of the Aphidbice, especially those 
which reside on trees, deposit eggs in the fall, and in this form hiber¬ 
nate. is beyond doubt true. But this method is impossible in the case 
of those which live upon annuals that perish with the close ot the 
season. It follows therefore that their eggs, it this is their method 
of hibernating, must be deposited somewhere else than on the plants 
they inhabit. It has been supposed by some that these are placed on 
the* earth. But this is contrary to the usual habits of insects, as the 
e<->■ ^s are, as a verv general and almost universal rule, deposited where 
the young can find food as soon as they appear. 
If deposited in the earth, this would, in the large majority of cases, 
place them where they would not be likely to find the kind of food 
necessary for their sustenance. It follows therefore, I think, as an ab¬ 
solute necessity, that some other method must be adopted. A hat is 
this? Although as yet not positively known I think a fact now as¬ 
certained may at least give us a clue to this mystery. 
It is now known that a number of species in the different groups 
are subject to dimorphism, that is to a change in form and mode of 
life to a certain extent. For example the Wooly Aphis of the apple 
tree, ( Schizoneur<i lanif/evci) is found upon the trunks of these trees 
and also on the roots; the same is also true of the Corn plant louse 
(Aphis maiclis) ; the Grape Phylloxera ( Phylloxera vitifoliae or P. vas- 
tcitrix Planch), resides a part of the time in galls on the leases and 
part of the time on the roots of the vine. Although the differences 
between the root and aerial forms are not equally marked and dis-^ 
tinct in all these species, yet the differences in situation and modes of 
life warrant us in concluding that they undergo certain physiological 
changes sufficient to adapt them to the changed circumstances. Ive- 
cent investigations have convinced me that these changes from aerial 
to root-inhabiting forms is not so rare as hereto supposed; and in fact 
I am led to believe that it will ultimately be ascertained that many 
which are now classed as apterous root inhabiting species aie but the 
dimorphic forms of aerial species. 
The term “Dimorphism” is used to express the fact that a species 
is subject to certain influences or changes which cause it to appear in 
a form different from that which is considered its normal appearance, 
or in other words that the species presents two forms. Some species, 
as the Graple Phvlloxera are “polymorphic,” or present three or more 
i forms. The term” “form” here is used to express any differences which 
might be used as specific in other cases, or as varietal, it is some- 
| times even used to indicate a wide difference in habits, but then it is 
i on the assumption! that such differences in habits will be accompanied 
by anatomical or morphological differences. Io explain moie cle<ul> 
to those who have paid little or no attention to entomology, and to 
render the explanation applicable to the particular point betoie us, I 
i call attention to the following fact. In some cases a species which 
