90 Proceedings of the Royal Physical Society 



find it by the sides of streams and ponds, on moor and waste land, and on 

 links by the sea. The results of one test examination are perhaps worth 

 giving. A small, low-lying field beside a well-preserved loch was searched, 

 and linings taken from the following nests : — Pheasant (1) ; Tufted Duck (2) ; 

 Shoveller (2) ; Mallard (2) ; Snipe (1) ; Redshank (1) ; Lapwing (2). In the 

 case of every species but one (Tufted Duck, whose nests contained no fleas), 

 garei was found. In the same field garei later occurred on a specimen of 

 the Meadow-Pipit. 



Borealis, insularis, and rothschilcli have not yet been taken in sufficient 

 numbers to justify remark. 



One might then, with reservations, propose the following categories to 

 exhibit the relation between these bird fleas and their hosts. 



A. Strictly monoxenous, e.g., styx. 



r Indiscriminately, e.g., gallinulw. 



B. Polyxenous ■< Attached usually to an order of birds, e.g.,fringillce. 



v. Infesting nests in certain localities, e.g., garei. 



The possibility of casual occurrences, e.g.,fringillce in Martins' nests, has 

 constantly to be borne in mind. Such cases are not always easily recognised. 



A classification like the above, of course, only groups the facts con- 

 veniently. The cause of the attachment of a Ceratophyllus to its host must 

 be deeper. Many explanations are possible, the simplest conceivable being 

 that the blood of a particular bird proves agreeable to some flea. It may be 

 looked for again in modifications of mouth parts, claws, or the like to suit a 

 certain type of skin, or (as I am inclined to think is the case with styx) the 

 parasite's habits may be nicely adjusted to those of the host. Temperature, 

 etc., may also play some part in regulating distribution. 



Ceratop>hylli are not met with on birds themselves with the frequency 

 one would expect from their almost universal occurrence in nests. 1 This is 

 not to be explained away by the fact that fleas leave their host after death 

 whenever the body begins to cool. During last year I have examined a 

 number of newly-shot birds, which had been forwarded in bags so securely 

 sealed that not even tiny acarids escaped. Nearly all these specimens were 

 more or less infested by Mallophaga, a considerable proportion carried 

 acarids, bid less than 10 per cent, harboured Ceratophylli, and then seldom more 

 than one or two examples. Of nests, probably 75 per cent, held some kind of 

 fleas. It is a matter of regret that I cannot quote exact figures, as no record 

 of the blanks has been preserved. But that the discrepancy referred to 



1 The Grouse Commission in examining thousands of birds encountered very few 

 fleas. See " Ectoparasites of the Red Grouse (Lagopus scoticus)," hy A. E. Shipley, Proc. Zool, 

 Soc. Loud,, pp. 325, 326. Aug. 1909. 



