KOCH. 
63 
scription of one hundred and one species of British 
Aphides. From time to time he continued to furnish 
notes on the same subject to the pages of the ' Zoologist ’ 
and the ® Entomologist/ In my diagnosis of species I 
shall make repeated references to these communica- 
tions. 
In the ^ Gardeners’ Chronicle ’ may be found various 
short notices on the ravages of different kinds of 
Aphides from the pen of Sir Oswald Mosley. 
In the . year 1857, shortly after the death of the 
author, appeared a complete monograph by 0. L. Koch, 
entitled, * Die Pfianzenlause Aphiden/ In this work 
every species that came under his observation is illus- 
trated by coloured copperplate figures. These drawings 
doubtless have a certain value, as they serve to direct 
the eye towards a general grouping ; but as they show 
no really correct outlines of the insects, and have the 
common fault of being gaudily coloured, the illus- 
trations m.ust be regarded only as small helps towards 
the identification of difficult species. Apart from 
these drawbacks, the monograph is an important one, 
and is of much value on account of the full descriptions 
it contains of each insect in its different stages. The 
treatise is all the more valuable to the student on 
account of the addition of numerous footnotes from 
the pen of Professor Kaltenbach. 
We need not wonder that such a difficult and variable 
family as the Aphididm should give rise to somewhat 
discordant opinions as to what ought to constitute 
real specific differences amongst them. I believe., 
although many previously undescribed insects are con- 
tained in Koch’s long list of 213 German species, that 
many of the forms he introduces are only variations 
caused by such external conditions as altered food 
and tem.perature. That such conditions have a strong 
modifying influence on Aphides Kyber* has shown. 
He remarked that, although the duration of the 
state of viviparition is in a certain sense almost 
* Kybei's * Einige ErfaKrungen tmd Bermerkungen iiber Blattlause.’ 
