An Account of the Bird-lice of the Genus Docophorus. 151 
organism and secondarily a species or group of species. As Prof. Kellogg in a 
recent brilliant resumé points out: “ Each host individual is in a way a small 
island biologically considered, with its inhabitants more or less nearly 
completely isolated from the inhabitants of other islands” (V. L. Kellogg, The 
American Naturalist, vol. xlvii., March 1913, p. 134), and the comparison is just 
if we add that these islands have an almost unchanging climate, wander about 
in space and occasionally come into contact, and finally are subject to 
periodic cataclysms which, if they do not destroy the inhabitants directly, at 
least set very many adrift to shift for themselves. We want to know what 
is the average population of these “islands”? what is native in it? what and 
how derived is any alien element present ? How far, again, does the population 
fluctuate seasonally ? How far do individual birds carry what may be termed 
family strains of a particular species of parasite ? and to what extent does the 
mixing of hosts lend towards uniformity in the characters of their parasites ? 
What is the age of a species of Docophorus?—and so on. It is evident that 
an ideal record would comprise very many items. It would include a census 
of the parasites (species and numbers) found; and an exact analysis of the 
stages (egg ; larva or immature; imago) represented; the state of the hosts’ 
plumage, age and date of capture; a note on the hosts’ habits and state 
of health, ete. It is only after much laborious spadework of the above 
description that anything may be expected of this field. But chiefly there is 
need at present of a more accurate definition of names, especially of the 
species of older authors. The host distribution of some of the commonest 
forms requires clearer determination. It is in the latter respect that it is 
hoped this contribution may prove of service to workers. 
Some notes, relevant only to the present inquiry, may be given on the 
species of Docophorus which have been described or recorded from Auks. 
Nitzsch named the parasite of <Alca torda, D. celedoxus. This 
species, mentioned by Burmeister in his “Handbuch” (1839), was again 
recorded by Denny (1842) from <Alca torda, Uria troile, and Fratercula 
arctica, At the same time the English author described three new species— 
D. platygaster from Uria troile, D. megacephalus from Uria grylle, and 
D. merguli froin Mergulus alle. Giebel (1874) adds little beyond describing 
more accurately than Denny the characters of Nitzsch’s species, of which 
the types were before him. Piaget (1880), who remarks of D. celedoxus, “Sur 
une Alca torda, une Uria troile et selon Giebel sur une Fratercula arctica,’ 
gives a good but very general account, and an excellent figure of the head 
of the species (he figures also the female genital mark), but his measurements 
seem to be taken from a small example. Lastly, in 1896, Kellogg described 
two new species, viz. D. calvus from a variety of the Common Guillemot, and 
