APHIS. 
172 
cannot be too much on their guard against the 
vvhole tribe of Aphides; for with what pleasure 
can a large choice collection be viewed, when 
there is scarcely a plant but what exhibits symp- 
toms of disease occasioned by vermin?” 
“ As the species of this genus are very numer- 
ous, and afford but few marks of distinction, 
Linmeus has contented himself with giving most 
of them trivial names according to the particular 
plant on which they are found: a close attention 
to them will however disclose more distinctive cha- 
racters than naturalists are aware of. Of some of 
the circumstances attendant on the propagation of 
these minute animals accounts are related, de- 
viating so wonderfully from the common course of 
Nature, that they could not be credited, were not 
the authors of them known to be men of the nicest 
and most accurate observation, and of the strictest 
veracity. On this part of the subject I have little 
to say from my own observation, but as some ac- 
count of so extraordinary a part of their hi.story 
may be expected in a paper of this sort, I shall 
state the facts, simply observing, that neither in 
the jlphis Salicisy which at times I have watched 
with great attention, nor in any other species of 
Aphisy did I ever observe any sexual intercourse 
to take place. Whether this may have arisen from 
the extreme infrequency of such a procedure, or. 
from my not having observed these insects at a 
proper time of the year, I know not; but most 
undoubtedly such intercourse does not take place 
between the different sexes of Aphis as in other 
