THE MALLOPHAGA AS A POSSIBLE CLUE TO BIRD PHYLOGENY. 



By LAUNCELOT HARRISON, B. Sc. 



In taking up a study of the Mallophaga, or Biting Lice, which are chiefly, though not 

 entirely, parasitic on birds, after a number of years of study of the hosts themselves, my 

 attention was very early directed towards a very remarkable correspondence betweeen the 

 species-groups of these parasitic insects coming from definite host-groups. Thus I found that 

 a species of Philoftcrus from the common Australian cuckoo Cacomantis flabelliformis was 

 hardly specifically distinct from the parasite of the European cuckoo Cuculus eanorus. Vet 

 these two birds have widely diverged from one another in their progress from the common 

 ancestral stock. In addition, these parasites, with others from other species of cuckoos dis- 

 tributed throughout the world, form a definite group within the genus Philopterus, which is 

 easily recognisable on its structural characters; so that one ma« say at a glance that any one 

 of the species has come from a cuckoo. Similarly, species of Philoptenis obtained from King- 

 fishers of different genera, and of world-wide distribution, have definite features in common 

 which enable them to be recognised both as showing close relation one to another, and as 

 having come from Kingfisher hosts. 



So far, I have only instanced two picarian families, but when the distribution of para- 

 sites among the orders of birds is studied, it is found that the same relation holds. Mallo- 

 phaean parasites of hawks, ducks, pigeons, or shore-birds, all afford well-defined groups, the 

 distribution of which is confined to, in most cases, a single host order. So much is this the 

 case, that Piaget (1880), in his great monograph, has divided up the unwieldy Mallophagan 

 <?enera into a number of sections; in the first place quite frankly upon host distribution, but 

 he has nevertheless been able to give diagnoses for these groups based upon their structural 

 peculiarities. 



In seeking for an explanation of this condition of distribution. I was forced to the 

 conclusion that the parasites, owing to the equable conditions of temperature and nutrition 

 under which they lived, had not tended to differentiate at the same rate as their hosts. The 

 Mallophaga do not voluntarily leave the body of their host, and cannot live awav from it for 

 more than a few hours. Their whole life is thus passed upon the body of the bird (or 

 mammal), the temperature of which is constant. Similarly they feed upon barbules of feathers, 

 epidermal scales, &c, which have a fairly constant chemical composition. And they undergo 

 no particular struggle for existence, as they are rarely found upon any one host individual 

 in such numbers as to render the obtaining of sufficient food a matter of difficulty. The 

 stimulus to a rapid differentiation is therefore absent, and the usual fluctuating variations 

 exist comfortably side by side, none tending to become dominant at the expense of the others. 

 There are some other interesting points in the biology of the Mallophaga, which are admir- 

 ably summarised by Kellcgg (1013. pp. 130 sqq.). 



The same author has also (1896, p. 51) come to the conclusion put forth at the beginning 

 of the last paragraph. He writes: — "The occurrence of a parasitic species common to 

 European and American birds, which is not an infrequent matter, must have another explan- 

 ation than any yet suggested. This explanation, I believe, is, for many of the instances, 

 that the parasitic species has persisted unchanged from the common ancestor of the two 

 or more now distinct but closely allied bird-species." 'And again, less cautiously (1913, p. 

 157) : — "Now, removing all cases of even an imaginable rare possible contact of bodies be- 

 tween these related but specifically distinct hosts, such as might occur in birds of circum- 

 rolar range, or in gregarious maritime kinds, meeting on common mid-ocean islands, or in kinds 

 occasionally exported by man from their normal range, etc., there are still left many cases of 

 this commonness of a parasite species to two or more usually rather closely related host 

 species of quite distinct geographic range. How can this actual condition be explained? 



