NO. 8 PARASITES— METCALF 9 



In 1905 Kellogg writes : 



From this fact of near relationship of hosts in all the cases of parasite species 

 common to several host-species it seems almost certain that this common oc- 

 currence, under circumstances not admitting of migration of the parasites from 

 host to host, is due to the persistence of the parasite species unchanged from 

 the time of the common ancestor of the two or more now distinct but closely 

 allied bird-species. In ancient times geographical races arose within the limits 

 of the ancestral host-species ; these races or varieties have now come to be 

 distinct species, distinguished by superficial differences in color and markings 

 of plumage, etc. But the parasites of the ancient hosts have remained unchanged ; 

 the plumage as food, the temperature of the body, practically the whole envi- 

 ronment of the insect, have remained the same ; there has been no external factor 

 at work tending to modify the parasite species, and it exists to-day in its ancient 

 form, common to the newly arisen descendants of the ancient host. 



Again in 191 3 and in 1914 Kellogg cited the same data, and also 

 other similar conditions for the Mallophaga and Anopleura (sucking 

 lice) of mammals and urged further collection and compilation of host- 

 parasite data for these hosts and parasites. 



Kellogg writes (1913) : 



From the three Acarinate or Ratitian bird orders the Rheiformes, or South 

 American rheas, the Casuariiformes or Australian cassowaries, and the Struthi- 

 oniformes or African ostriches, only five species of Mallophaga have so far been 

 recorded. On the rheas occur three species of Lipcurus, one being found on each 

 of two host species and the other two on a third. On one species of AustraHan 

 cassowary are found two Mallophagan kinds, one of which is the same species 

 as that found on two of the South American rheas, while from the African 

 ostrich, Struthia caiuclus, are recorded two parasite species, one of which is 

 the same as that found on the third rhea. 



It is clear that Kellogg, like von Ihering, saw the value of evidence 

 from parasites as to genetic relationships between hosts, and as to 

 recent and ancient dispersal of the hosts. The importance of such 

 evidence in paleogeographical studies was not mentioned by Kellogg, 

 but was implicit if not expressed. Since he makes no reference to 

 von Ihering's studies, Kellogg seems to have reached independently a 

 realization of the important aid parasites give in the study of genetic 

 relationships and of zoogeography. 



In 1909 Williams published a paper on the great epidemic among the 

 Indians of New England in the years 1616-1620. The following 

 quotation shows that he had a view of the bearing of parasitic disease 

 upon questions of the origin and dispersal of human races and he 

 paralleled Kellogg's conception of commimity of parasites among birds 

 indicating common ancestors : 



From this point of view [of geographical origin and distribution] it is of 

 interest to study the relation of the American race to infectious diseases. Any 



