554 INVESTIGATION OF INSECTS. 
cies appear at first very slight, and require a practised 
eye to catch them, yet it occasionally happens that con- 
siderable apparent differences may safely be disregarded. 
The colour of insects,—to which unhappily for want of 
better characters we are so generally forced to have re- 
course,—though usually constant, is in some species very 
variable*. This is the case sometimes with whole colours. 
Thus Carabus arvensis, Pcecilus cupreus, &c., are some- 
times of a copper colour; at others, resemble brass; at 
others, they are green or blue, and even black. ‘The 
colour of spots also often varies. In some individuals 
of Pentatoma oleracea they are pale, and in others red. 
The number and shape of spots are also often incon- 
stant. Many of the species of Coccinella so abound in 
these variations, that nothing short of the most careful 
examination can enable you to distinguish the species 
from the variety. Insects vary also in szze: but as this 
is never assumed as a specific character, it will not oc- 
casion you much trouble. Where the difference in this 
respect between two specimens is very great, the pre- 
sumption is that they are specifically distinct. Diffe- 
rences in sculpture and proportion do not always indicate 
different speczes; this being sometimes, as we have seen 
above, only a sexual character’. Authors also in their 
descriptions in this respect sometimes mislead the young 
student. When Linné calls the thorax of Aphodius er- 
raticus smooth (levis), he would not expect to find it co- 
vered with impressed puncta, and with a longitudinal 
posterior impressed line. Likewise in describing Chicenia 
estita and nigricornis, Fabricius passes without notice 
20/7 in WP 
* See above, pe ouy- Vou. ILL. p. 303. 
