556 PHYSIOLOGY". 



contrary, Motacilla, AnLhus, Certhia, Muscicapa, and Hirundo, de- 

 vour insects only, namely, flies and larvae. Among the Cuckoos it is 

 especially the large genera of Cuculus and Picus which attack insects, 

 and Upupa, Epimachus, Merops, and many exotic ones ; whereas the 

 genera Rhamphaslus, Buceros, and Psittacus prefer vegetable food, 

 particularly fleshy fruits, to insects, and therefore feed chiefly or exclu- 

 sively upon them. We besides find among the snipes many genera 

 which feed upon insects and preferably upon their larvae, for instance, 

 Charadrius, (Edicnemus, Scolopax, Tringa, and Totanus, particu- 

 larly their smaller species ; the other waders and water birds prefer 

 to insects as food the amphibiae, molluscae, fishes, and other marine 

 animals. 



309. 



We find a similar relation between insects and the mammalia. Many 

 of them are inhabited by parasitic insects, which either belong to the 

 already mentioned genera Trichodectes and Gyropus among the Mallo- 

 phagi, or come under the genus Pediculus, peculiar to the mammalia. 

 The genus Pulex also lives principally upon the mammalia. Among 

 these also may be classed the pupiparous genera of the Diptera, which 

 family is also distributed upon both classes, yet only upon individual 

 species, and lastly, the family of the (Estrodea, which is peculiar to 

 the mammalia. Trichodectes and Gyropus likewise devour the soft 

 woolly hair of the mammalia, and perhaps also their epidermis ; whereas 

 the lice, by means of their hooked proboscis, which they thrust through 

 the integument, suck their blood. Many species of them are found 

 upon very many mammalia, for instance, upon the Glires, Ruminantia, 

 and swine, but not upon all. The genus of the flea is parasitic only 

 in its perfect state, as a larva it lives in putrid substances, especially 

 in dirty sleeping apartments, in the stalls of animals, &c. The flea 

 lives upon men, bats, beasts of prey, Glires, and they have even been 

 found upon pigeons and swallows ; they were all formerly classed under 

 one species, which Linnaeus called Pulex irritans, but they have since 

 been correctly separated into several species *, and characterised, as is 

 usual among parasites, according to the animal they inhabit. I have 

 myself only yet closely examined the flea of the rat, and I have found it 

 distinct from that of man. Among the Pupipara, the genus Hippo- 

 bosca (Nirmomya, Nitz.), of which only one species, the H. equina, is 



* .1. F. Stephens' Catalogue of British Insects. Loml., 18'J.O. ovo. Part 2, p. Si'!!. 



