Book-lice and Bark-lice; Biting Bird-lice 115 



maturity. There is never, in young or old, any sign of wings or wing-pads. 

 The body is flattened, so much so indeed that it is difficult to hold a live 

 specimen securely between thumb and finger-tip. The body-wall is strongly 

 chitinized, and is firm and smooth. The markings are often very distinct, 

 and sometimes bizarre, but the coloration varies only from white to black 

 through various shades of pale yellowish brown, tawny, reddish brown, and 

 blackish brown. The antenns are short and in one suborder (see classifica- 

 tion key) are wholly concealed in pits or grooves on the under side of the 



Fig. 144. — Immature and adult stages of the biting bird-louse, Lipeurus jorficu/alus, 

 taken from a pelican, i, adult female; 2, adult male; 3, very young stage; 4, 

 older immature stage. (Natural size of adult specimens j'j in.) 



flattened head. The legs are strong, and each foot bears two claws. These 

 small creatures run very swiftly. 



Perhaps the oddest thing about the structure of the Mallophaga is the 

 presence in the throat of the curious oesophageal or pharyngeal sclerite 

 already referred to in the account of the Corrodentia. This sclerite is a 

 sort of bonnet-shaped piece (Fig. 145) lying in the lower wall of the throat 

 and seems to be an arrangement for starting the little bitten-off pieces of 

 feather barbs straight, that is, lengthwise down the oesophagus! The bark- 

 lice and book-lice, which have a similar oesophageal sclerite, also bite off 

 and swallow small bits of hard, drv organic substance. 



