52 CALIFORNIA ACADEMY OF SCIENCES. 



Yolgas: Nirmus signatus and N. pileus found by me on 

 Recurvirostra americana were described by Piaget and 

 Nitzsch respectively from Recurvirostra avocetta, the 

 European Avocet; Lifeurus ferox taken by me on Dio- 

 medea albatrus is recorded by European writers from 

 Diomedea exulans, brachyura and mchuwphrys; Li pair us 

 forficulatus taken by me on Pelecanus erythrorhynchus 

 and P. californicus was described by Nitzsch from P. 

 onocrotalus; and similarly the most of the twenty-two 

 previously described species taken by me from American 

 birds might be thus offered as examples. We have in 

 all of these cases the common parasite occurring on the 

 American representatives of the genus to which the orig- 

 inal Old World host belongs. Looking now for the ex- 

 ceptions to this condition — namely, for instances where 

 the known species when found on an American bird is 

 found on one widely separated phyletically from the Eu- 

 ropean host — we find no clearly defined instance of this 

 condition, no instance where association during life or 

 " strangling " after death of the host can be put aside as 

 possible explanations of the presence of the parasite on 

 the unexpected host. 



There are to be noted other results of the influence on 

 the taxonomy of the Mallophaga of the peculiar condi- 

 tions of their parasitic life. While the uniformity and 

 persistence of the conditions under which the life of 

 the parasites is passed tends to preserve with little 

 change the species types, the peculiar isolation, often 

 pretty complete, of groups of individuals of a parasite 

 species on individual birds of the host species and the 

 consequent close breeding tend to foster and fix those in- 

 evitable slight variations always manifest in a comparison 

 of offspring and parents, but under normal conditions 

 held in check or lost (unless directly advantageous) by 



