NO. 8 PARASITES METCALF • 7 



V^on Ihering, in 1891, in discussing ancient land connection between 

 southern South America and Australasia, points out that once Pata- 

 gonia and Chile, on the south, were separated by sea from the Ecua- 

 dorean highlands and from the ancient plateau in eastern Brazil. 

 Adducing evidence that southern Brazil was then united to Chile and 

 Patagonia rather than to the Brazilian highlands, he writes : "Aeglca 

 lacvis [a freshwater decopod crustacean] occurs in Rio Grande do 

 Sul [southern Brazil] and in Chile and in hotJi places zvith the parasite 

 Tcmnocephala chilensis'' [an ectoparasitic flatworm].^ This, so far as 

 I can learn, is the earliest instance of using evidence from parasites to 

 reinforce evidence from their hosts in discussion of problems of 

 dispersal. 



In 1902 von Ihering made extensive use of parasite data in deter- 

 mining the place of origin of different South American vertebrates, 

 especially mammals, discussing whether they evolved in South Amer- 

 ica or arose north of the Isthmus of Panama and spread to the 

 southern continent. The data he used were from parasitic worms : 

 Acanthocephala, Trematoda (flukes), Cestoda (tapeworms) and Ne- 

 matoda (pinworms, etc.). In his discussion he makes the following- 

 points : 



Two species of hosts are of common descent if they are parasitized 

 by the same species or by nearly related species of parasites. 



North America and South America were not united as now until 

 Pliocene times. 



There are two classes of elements in the neotropical fauna, one 

 class autochthonous, a second class heterotochthonous, having been 

 derived from North America and having entered South America since 

 the beginning of the Pliocene period. 



The long isolation of the autochthonous South American mammals 

 during the Tertiary period should have developed in them species of 

 worms different from those in the heterotochthonous mammals, the 

 parasites of the latter showing resemblance to those of holarctic 

 mammals. 



The facts exactly agree with these theoretical considerations. Only 

 the autochthonous South American hosts carry peculiar species of 



^ Italics mine. 



^ I have distinct memory of reading years ago mention by von Ihering of 

 the genetic divergence between the freshwater mussels of southern and northern 

 South America and his saying that those of the Argentine and of southern- 

 most Brazil are like those of Southern Chile west of the Andes, and that they 

 have the same parasites, but search of those of von Ihering's papers now ac- 

 cessible to me has failed to yield this reference. 



