172 APHIS. 



cannot be too much on their guard against the 

 whole 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, 

 Linnaeus 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 history 

 may be expected in a paper of this sort, I shall 

 state the facts, simply observing, that neither in 

 the Aphis Salicis, which at times I have watched 

 with great attention, nor in any other species of 

 Aphis, 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 



