146 FLEAS, FLUKES AND CUCKOOS 



intermediate hosts, such as the flukes, which may show a false host 

 specificity due to the common habitat and diet of their hosts (ethological 

 specificity, p. 45). 



In conclusion it can be said that as a general principle the relation- 

 ships between the Mallophaga reflect those existing between their hosts. 

 Birds with a doubtful systematic position cannot be placed on the 

 evidence of their Mallophaga if only one genus of feather lice is 

 available from which to draw conclusions, for this may be an ancient 

 straggler or a relic. If, however, these birds harbour three or more 

 genera common to the birds of another order this may be taken as 

 strong presumptive evidence that the hosts in question belong to that 

 order. The flamingos are a case in point. The ornithologist should 

 accept the evidence from this source at least as a clue to relationship, 

 just as he accepts anatomical evidence of bone loss or the arrangement 

 of a muscle. Alone, any one point will not establish the position of a 

 bird of doubtful affinities, but the total sum of such evidence from many 

 sources may be overwhelming. In the future, when the feather Hce as a 

 group are as well known as the butterflies, the evidence from this 

 source may be of great significance in the study of the origins, relation- 

 ships and ancient distribution of various families of birds. 



The student of Mallophaga, in this aspect of his work, can be 

 compared to the palaeontologist. He delves into the past, not by 

 quarrying in the rocks for fragments of bones, but by studying the 

 morphology and distribution of these living fossils. As he pieces to- 

 gether the story of their evolution, he hkewise unfolds the story of the 

 evolution of the birds. 



The Mallophaga of the British Isles 



The distribution of the Mallophaga is, in general, a host distribution, 

 not a geographical one. The jackdaw, whether living in England, 

 Scotland, Germany or Scandinavia is parasitised by the same species of 

 hce. The Mallophaga of Britain are, therefore, the Mallophaga of 

 British birds. For this reason there is little object in fisting the feather 

 lice of any specific geographical area; attention should be concentrated 

 on the study of the louse fauna of a group of related birds, for such 

 groups are the equivalent of the geographical range of free-living 

 insects. This statement, nevertheless, needs qualification. There does 



