HOST PARASITIZATION 



53 



following: the Soricidae, represented by Sorex vagrans, S. montereyen- 

 sis and Neosorex bendirei; the Talpidae, represented by Scapanus lati- 

 manus and N euro trie hus gibbsi; the Zapodidae, represented by Zapus 

 orarius and Z. trinotatus alleni; the Aplodontidae, represented by Aplo- 

 dontia phaea; the Didelphidae (Marsupialia), represented by Didel- 

 phys sp. The number of individuals examined in each of the above cases 

 is for the most part very small, ranging from three in the case of Didel- 

 phys sp. to twenty-five or thirty in the case of the two species of Sorex. 

 For this reason it is extremely probable that some of these negative con- 

 ditions will be changed by further investigation. 



We have found no Anoplura, with the exception of one case pre- 

 viously discussed, on any of the Mustelidae, represented by two species 

 of skunks, Mephitis occidentalis and Spilogale phenax, one species of 

 badger, Taxidea taxus, and one species of weasel, Putorius xanthogenes 

 mundis. The Felidae, represented by two or three individuals of one 

 species, Lynx calif ornicus, and the Geomyidae, represented by perhaps a 

 hundred individuals of several species of the genus Thomomys, have like- 

 wise produced no Anoplura. All these species, however, are represented 

 in the Mallophagan host list. 



A few observations in regard to the occurrence of parasites upon 

 the individual hosts may perhaps be of some interest. Mjoberg has stated 

 that in general but one species of Anoplura occurs upon any host species ; 

 but this is by no means always the case. Many of the Sciuridae are reg- 

 ularly parasitized by two species of Anoplura, and probably sometimes 

 even by three; and the various species of the genus Microtus, of the Mu- 

 ridae, is regularly parasitized by two species. The white-footed mice of 

 the genus Peromyscus likewise harbor two Anopluran species, altho one 

 of these is evidently rather rare. It is, however, an interesting fact, 

 whether of any significance or not, that those host species which are the 

 most heavily parasitized by Mallophaga do not harbor any Anoplura ; 

 and the reverse is also true. The Sciuridae and Muridae, which collec- 

 tively harbor four or five genera and numerous species of Anoplura, do 

 not seem to possess a single Mallophagan species; and the Mustelidae 

 and Geomyidae, which have several species of Mallophaga and are in- 

 dividually very heavily parasitized, apparently do not normally possess 

 any Anoplura. 



The degree of parasitization of the individual hosts is extremely var- 

 iable ; but in general it may be said that hardly half of the host individ- 

 uals of a parasitized host species are sufficiently infested to permit of 

 finding the parasites ; indeed in many cases the percentage is even small- 



