Some Habits and Hosts of Bird Ceratophylli. 91 



exists (and it is a great one) can hardly be doubted. It is the more striking 

 since the birds, examined feather by feather, have been common species. Of 

 course, the absence of fleas from certain birds must be due to a great extent 

 to the preening habit. For exactly the same reason, it will be found that 

 species of .Docophorus (Mallophaga) live on some Passerines only on the 

 crown of the head and on the upper feathers of the throat. 



The number of Ceratophylli affecting a species of bird varies. Often in 

 the same nest two or more kinds occur. Gallince and Gallinulce is perhaps 

 the commonest combination 



The case of C. urbica is noteworthy, for this little bird is victimised by 

 no less than six Ceratophylli, if one includes gallince which has occurred with 

 the others. Between fleas, acarids, Stenopteryx hirundinis, and the Swallow 

 Bug, 1 Martins' nests must be rather lively nurseries. Leaving out of 

 account the casuals, gallince and fringillce, one might try to explain the large 

 number of Ceratophylli by supposing that the bird, a migrant which roosts 

 and breeds naturally on cliffs, etc., has in its passage through various lands 

 acquired new parasites from time to time. This can hardly be the true reason, 

 for C. riparia has only one species of flea attached to it, while H. rustica does 

 not seem to have even one, in Scotland at least. Gallince has occurred in 

 its nest, but surely by accident. 



It must be confessed that we know little as yet of the species of Cerat- 

 ophylli found on birds, — still less of the factors physiological, biological, and 

 possibly climatic that govern the relations between parasite and host. 



1 I have not met with this parasite in Scotland. 



(Issued separately, 6th April 1910. 



