INVESTIGATION OF INSECTS. 567 



insects, may also still be consulted; and thus many 

 mistakes rectified, which would otherwise greatly mis- 

 lead 3 . 



Though sometimes the limits that separate good spe- 

 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 5 . 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 size: 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 species , this being sometimes, as we have seen 



a It may not be amiss to mention a few i Sph&ridium dytiscoides 

 is a Hydrophttus related to H.fuscipes. S. glabratum is heteromerous, 

 probably one of the Helopii Latr. Carabus retusus and Maderce both 

 belong to Calosoma, Cistela angustata is a true Choleva. See Linn. 

 Trans, xi. 138. S. b See above, p. 406. 



