52 NORTH AMERICAN ANOPLURA AND MALLOPHAGA 



V 



DEGREE OF HOST PARASITIZATION. 



In addition to a record of the hosts upon which parasite species have 

 been found, it is very desirable to know also those host species which 

 have been examined for parasites with negative results. In fact if we are 

 to arrive at a proper understanding of the problems of species distribu- 

 tion among the parasites, then negative records are in many cases of an 

 importance almost equal to the positive records. Even though repeated 

 failures to find a certain parasite upon a certain host can never be re- 

 garded as absolute proof that that particular parasite does not occur up- 

 on that particular host, the record of such failures does at least give 

 much aid in judging whether our positive records of the occurrence of a 

 parasite species upon that host are to be accepted unquestioningly or are 

 to be regarded with suspicion. While straggling, or the accidental occur- 

 rence upon a host species of a parasite not normal to it, is not a very com- 

 mon occurrence, it does sometimes happen. The appearance upon a car- 

 nivorous host of parasites normally found upon the prey of that host, or 

 especially the transference of parasites from one host to another in the 

 game-bag or on the skinning-table may, and in fact do, sometimes occur. 

 In such cases, and in the case of parasites taken from skins in museums 

 and from hosts which have been confined in zoological gardens, negative 

 records, whenever available, are unquestionably of extremely great value. 

 Because of these facts we are adding what may very well be called a 

 negative host record, including only those host, species which we our- 

 selves have examined for parasites with negative results. 



We have found no Mallophaga upon any of the Sciuridae repre- 

 sented by several species and many individuals of the genera Sciurus, 

 Eutamias, Citellus, Callospermophilus, Arctomys and Sciuropterus, nor 

 upon any of the Muridae represented by the genera Peromyscus, Micro- 

 tus, Phenacomys and Mus. There have previously been isolated records 

 of the occurrence of Mallophaga upon certain Sciurids, but the evidence 

 indicates very strongly that neither the Sciuridae nor the Muridae nor- 

 mally possess a Mallophagan species. 



We have found neither Mallophaga nor Anoplura upon any of the 



