54 CALIFORNIA ACADEMY OF SCIENCES. 



the individuals from different bird individuals. While I 

 believe myself able to refer specimens taken from Amer- 

 ican birds to a score of species described from specimens 

 taken from European and Asiatic birds, in all of these 

 instances there are slight but recognizable differences be- 

 tween the American specimens and the type-forms of the 

 species (as well as I am able to make comparison, having 

 only the drawings and descriptions of these type-forms to 

 refer to). 



The differences in relative abundance or rarity of the 

 individuals of a species, and in the relative freedom or 

 seriously infested condition of the hosts may be referred 

 to briefly. Certain specific examples will serve to illus- 

 trate the various conditions. In the first place the host 

 species may have several parasitic species as Diomedea 

 albatrus, Fulmar us glacialis vars. glupischa and rodgersii 

 and Fulica americana, each with six species of parasites; 

 or the host species may have but one (very rarely) or two 

 or three parasitic species infesting it, as with most of the 

 ducks and gulls. A parasitic species may be constant in 

 its appearance on the individuals of its host species, as 

 Docophorus far/, almost certain to be found on any gull 

 specimen shot, Lipeurus ccler, which I found on twenty- 

 nine out of thirty specimens of Fulmarus glacialis vars. 

 >rlupischa and rodgersii examined, Dociphorus occidentalis 

 similarly found on twenty -nine out of these thirty Ful- 

 mars; or it may be found on but few individuals of the 

 host species, as Docophorus quadraticcps found on one of 

 fourteen specimens of Fulica americana examined, and 

 Nirmus pnestans found on two of fourteen specimens of 

 Sterna maxima examined. There may be many individ- 

 uals of a parasitic species always present on the body of 

 the host, as with Lipeurus ccler on the Fulmars, of which 

 parasite I have collected nearly one hundred specimens 



