126 BRITISH APHIDES. 



had been cut some weeks, I found P. laducarms very 

 abundant at the roots of the wheat stubble. These 

 apterous insects were full of embryos, ready for extru- 

 sion. Although Persicaria and other weeds were in the 

 neighbourhood, the roots of which I carefully searched, 

 I could find no Aphides of other species. Siphono- 

 pliora granaria is such a common corn pest that I 

 thought some underground form might possibly pre- 

 sent itself, to explain the total disappearance of the 

 insect at the gathering in of the crops. However, 

 nothing discovered led me to believe in such an under- 

 ground habit of ^S'. granaria. The different winged 

 forms of course precluded all likelihood of any con- 

 nection between this Aphis infesting the ear and the 

 Pemphigus nesting at the root of the wheat. 



Specimens of these last were kept in moist earth 

 under a bell glass for many days, but I failed in pro- 

 curing either images or pupa3 from them. 



The large females are well suited for showing the 

 fine net-work of tracheae which ramifies throug^hout 

 the body. These air-tubes may be readily separated 

 by teasing with fine needles, after the insect has been 

 placed in syrup or a weak solution of salt, to prevent 

 the breaking-up of the delicate tissues. 



It is not easy to see why Koch separated this and the 

 preceding P. fuscifrons from the genus Pemphigus, 

 His genus Ami/cla seems to depend on characters too 

 indefinite and variable to allow of certainty. He seems 

 to rely chiefly on slight variations of length in the 

 antennee and rostra in the three species he describes 

 in his genus. 



