FEATHER LICE 1 47 



seem to be in some cases a true geographical distribution superimposed 

 on the host distribution. A higher percentage of infested individuals 

 may be found in parts of a bird's range, and certain species of lice seem 

 to be absent from their host in some localities. The pouch-louse, found in 

 all the pelicans (Pelecanidae), has been recorded from the related cormor- 

 ants (Phalacrocoracidae) from the New World and Antarctic species, 

 but never from those of Africa and Europe. 



We have already seen that each bird species supports the repre- 

 sentatives of a number of genera of feather lice ; some birds may 

 also harbour two or more species belonging to one genus. The 

 sanderhng has five, the rook may have six and one of the S. 

 American tinamous is parasitised by the bewildering number of 

 twenty-one species belonging to twelve genera and three famihes. 

 Although many of the species of Mallophaga are found on more than 

 one kind of bird it follows that there must be a large number of them in 

 the world. Of these probably less than half have been named, and 

 many not even collected. The number of species hkely to be found on 

 the 400 or so birds on the British list can only be estimated within wide 

 limits, say 500 — 1,000. Again, a number of these still has no valid 

 scientific name ; even two of the Hce from the common rook are un- 

 described and consequently are still nameless. There are few specialists 

 working on the group, for it is of no medical and of Kttle economic 

 importance. Hidden as they are in the plumage of the bird, feather 

 hce do not attract the immediate attention of the naturalist and few 

 people even know that they exist. Moreover, they are difficult to 

 collect, and when collected must first be treated and mounted on 

 glass slides and then examined under the microscope. Species are 

 distinguished from each other mainly by the details of the male 

 genitaha, which for microscopic study must be dissected and mounted 

 separately. When the louse is ready for identification it is first 

 necessary to know whether it has already been described or named. 

 This is not easy. The early authors — the first figures were published in 

 1668 by the great Itahan biologist Redi— did not realise the importance 

 of the small characters necessary for separating species, so that their 

 descriptions and figures can only serve to identify the genus, and that 

 sometimes doubtfully. Nor did the early authors always name the host 

 from which they took the louse, or they recorded it from three hosts, 

 which are now known to harbour three distinct species office. Lastly, the 

 systematics of the Mallophaga are cursed by records of straggling feather 



FFC— L 



