On the Geographical Distribution of Insects. 335 



nected with that of the plants of the genus Souda. 3d, 

 Brackish waters. These have also a small number of peculiar 

 species, such as the Hydrcena marina, which is not found in 

 the sea, as its name woidd lead us to expect. According to 

 Kirby and Spence, it is only in dried salt-marshes that we 

 find certain Hemipterous species of the genus Acanthia (A. 

 saltatoria, littoralis, zosterce. Sec.) 4:th, Fresh waters. Among 

 the species which inhabit these, some live completely im- 

 mersed, and may be divided into such as continue there only 

 in their earlier states (CuUcidce, Libellulidce, Phryganice, 

 Ephemerce, &c.) and such as pass their whole life in them, 

 Hydrocantharidce, Hydrophilus, Nepa). The latter can leave 

 their watery abodes for a short time (which they usually do 

 at the approach of night), and thus they partake of the nature 

 of aquatic, terrestrial, and aerial animals. The other aquatic 

 species, although living in the water, are unable to swim, and 

 are usually found clinging to aquatic plants. Such are the 

 Hydrcence, certain Sphoiridia, and a few CurcuUonidoe of the 

 genera Bagous, Hydronomus. The circumstance of waters 

 being either stagnant or running, has an influence on the 

 species inhabiting them. For example, the greater part of 

 the Dytiscidae frequent ponds and marshes, in preference to 

 rivers, while the opposite is the case with Gyrinus, Haliplus 

 elevatus, Macronychus, &c. bth. Margins of fresh waters. 

 The species met with in such situations, differ with the nature 

 of the soil. If it be sandy, we then find Omophron, which dig 

 into it a few inches beneath the surface. Chlaenius and Bem- 

 hidium select what is stony and mingled with gravel ; if it be 

 muddy, it is adapted to Elaphrus, Helophorus, Parnus, &c, 



Qth, The various kinds of soil, which form an extensive ca- 

 talogue, according as they are dry or moist, cultivated or un- 

 cultivated, rocky, sandy, compact, light, &c. have each their 

 appropriate insects, which either inhabit the surface or the 

 interior. The former are said to be epigeous, the latter hy- 

 pogeous. 1th, Mountains. Their declivities afford numerous 

 stations for insects. The species which live near the sum- 

 mits, are called alpine, such as inhabit their lower stages, 

 subalpine. But these epithets are only applied with propriety 

 when the species are not found, or at least are very rare in 



