6o 



FLEAS, FLUKES AND CUCKOOS 



genera of feather lice common to some possibly related group of birds, 

 wc consider the evidence of relationship strong — for three major 

 errors in the interpretation of louse morphology would be improbable. 

 In all cases, however, the evidence presented by both host and parasite 

 has to be carefully examined and sifted because of other factors (see 

 p. 141) which may be involved. As yet there is little co-operation 

 between one type of specialist and another. There is a natural 

 tendency for the ornithologist to place more reliance on the work of his 

 fellow bird specialists, which at least he can appraise, than on that of the 

 entomologist and helminthologist, and frequently he rejects out of hand 

 the valuable evidence provided by the parasitologists. 



The fleas, unlike the feather lice, have only been associated with 

 birds for a few hundred thousand years (see p. 90), and through them 

 we can study quite another aspect of parasitism — namely the effect 

 on the parasite of the change to a new type of host. 



In the following account of the Mallophaga and the Aphaniptera 

 we have concentrated on the British fauna, but it must be realised that 

 numerically the two groups are not comparable, for the former contains 

 about 1,500 species in Britain, and the latter about a baker's dozen. 

 Consequently, while it is quite possible to give a very brief account of 

 the various species of bird fleas, the feather lice have to be treated in a 

 more general manner. 



'* The intromittent organ of fleas is probably the most complex 

 genital apparatus to be found in all insects.'* 



