FEATHER LICE 133 



is the fold of the head, which envelops the antennae, and is probably 

 a modification to protect these structures when the louse is moving 

 rapidly through the feathers. A somewhat similar device is found in 

 several other groups of ecto-parasites. 



Two unusual ecological niches have already been mentioned — the 

 throat-pouches of pelicans and cormorants occupied by the genus 

 Piagetiella and the quills of the wing-feathers of the curlew by a species of 

 Actornithophilus . The fact that these two are members of the less specialised 

 Amblycera suggests that the occupation of the two niches is compara- 

 tively recent. The limited distribution of the pouch-louse within the 

 order Pelecaniformes and of the quill-louse within the order Charadrii- 

 formes also supports the idea of a relatively recent colonisation of these 

 two habitats. 



Many of the problems confronting systematists are caused by 

 animals leaving their original ecological niche in favour of another. 

 They subsequently develop characters which adapt them to their new 

 environment : these are superimposed upon, and more or less obliterate 

 the original characters which would form the basis for their scientific 

 classification. The flamingoes probably illustrate a case of this kind. 

 They are placed by most ornithologists with the storks and herons, but 

 by a few with the geese and ducks. There are convincing arguments to 

 support each theory. The evidence provided by the Mallophaga on 

 the systematic position of these long-legged ducks or duck-billed storks 

 will be discussed later. Our knowledge is still insufficient to enable us 

 to recognise all the genera of Mallophaga which have possibly changed 

 their ecological niches, but there seems little doubt that this has 

 happened in the case of one genus on the passerine birds. The head 

 louse {Philopterus) of passerine birds is a typical inhabitant of the head 

 niche — with a short round body and large head (as in Plate XXI). 

 The starlings, however, lack a typical passerine head louse, but a 

 species (Plate la) is found on the head which resembles it in general 

 body form. A detailed examination of this species shows that it is, in 

 fact, more closely related to another genus of body louse with a small 

 head and a more elongated body, also found on the passerines. It is 

 tempting to speculate that the original passerine head louse on starlings 

 became extinct, for some unknown reason, and that the empty ecologi- 

 cal niche was filled by members of another genus which have now 

 assumed the general body form of a typical head louse. 



