NEW MALLOPIIAGA. 5 1 



species of Mallophaga referred to in this paper as being 

 taken on American birds one -third are referable to spe- 

 cies previously described from European or Asiatic birds), 

 must have another explanation than any yet suggested. 

 This explanation, I believe, is, for many of the instances, 

 that the parasitic species has persisted unchanged from 

 the common ancestor of the two or more now distinct but 

 closely allied bird-species. With the spreading of the 

 ancestral bird-species, geographical races have arisen 

 within the limits of the species which have, with time and 

 isolation caused by newly appearing geographical barriers 

 (due to geologic or climatic changes), come to be dis- 

 tinct species — species often distinguished only by super- 

 ficial differences in color, etc. The parasites have re- 

 mained practically unaffected by the conditions which 

 have produced the differences among the birds; the tem- 

 perature of the host's body, the feathers as food, all of 

 the environment is essentially unchanged in its relation 

 to the parasite. The parasitic species thus remains un- 

 changed, while the first Larus species or Anas species 

 becomes differentiated into a dozen or score of specific 

 forms, all with' a common parasite. 



In substantiation of this explanation of a common pos- 

 session of a parasitic species by Old and New World 

 birds some examples may be referred to. As already 

 mentioned, I have found on Fulica americana the same 

 species of parasite, Docophorus pertusus, described by 

 Nitzsch from specimens taken from the European Fulica 

 atra; Docophorus melanocephalus taken by me on Sterna 

 maxima is recorded by European authors from Sterna 

 caspia and S. cantiaca; Nirmus punctata*, found by me 

 on Larus occidentalis was described by Nitzsch from 

 Larus ridibundus and has been found by Piaget on Larus 

 dominicans from Chile and on Larus ichthy&tus from the 



