V °'sw VI ] Kellogg, Some Parasites of Birds. 235 



for example, the case of the Mallophagan species Nirrnus siguatus 

 and Nirmus pileus found in Europe on Recurvirostra avocetta and 

 in America on Recurvirostra americana. The instances in which 

 the parasites are common to hosts of different genera in America 

 and Europe are not infrequent but the genera are, in almost all 

 cases, allied ones. 



I have suggested elsewhere the only explanation of this prob- 

 lem in the distribution of the Mallophaga which seems to me pos- 

 sible, and that is that the Mallophagan species common to hosts 

 of different species, in instances where all possibility of direct 

 migration is precluded, have persisted unchanged from a host 

 which was the common ancestor of the present distinct host 

 species. The influences, climatic and geographic, which have 

 resulted in effecting the founding of the new bird species have 

 had no effect on the parasitic species. The food and environ- 

 ment of the parasite are essentially the same on one bird as on 

 another. A paling of plumage, a shortening of legs, a develop- 

 ment of crest feathers, or whatever new characters might be fos- 

 tered and fixed by a change of environment of the host, resulting 

 in the production of a new bird species, would have, apparently, 

 no necessary influence on the parasite. Does some more prob- 

 able explanation of the facts of distribution of these bird para- 

 sites suggest itself to any member of the A. O. U. ? 



It may be of interest to append a few notes regarding the rel- 

 ative abundance or rarity of the parasites on their hosts, and 

 regarding the constancy or irregularity with which a specific para- 

 site is found upon its special host. A host species may have 

 several parasitic species infesting it ; I have taken ten species of 

 Mallophaga, representing six genera, from Puffinus opisthomelas, 

 and twelve species representing five genera from Fulica ameri- 

 cana. Or, the host species may have but one or two or three 

 species of parasites, as is the case with the Ducks and Gulls. 

 A parasitic species may be constant in its appearance on the 

 individuals of its host, as with Docophorus lari Denny, almost 

 certain to be found on any Gull shot, or it may be found on but 

 few individuals of its host species, as with Docophorus quadra- 

 ticeps Kellogg, found rarely on Fulica americana. There may 

 be many individuals of a parasitic species always present on 



