A«i-20. STUDIES OF THE BITING LICE EWING. 37 



ford Expedition to South America, observed live sloths, several of 

 which were killed and examined for lice but with negative results. 



A survey also of the records for the different host families causes 

 us to accept with very much reservation the records for two host 

 species belonging to the order Kodentia. The single record from 

 the Sciurid host has already been discussed. There remains for 

 consideration the record of Protor/yropus norjnalis Ewing from a 

 species of Oryzomys^ a member of the family Muridae. This record 

 is based upon the obtaining of a single specimen from a recently 

 dried skin. Although many other Murid skins, taken from the same 

 region in South America and at the same time, were examined, no 

 other Gyropids were obtained. On the other hand this same louse 

 was taken in some numbers from two Cavia skins, thus, here is an 

 indication of its true host relationship. 



SIGNIFICANCE OF THE GEOGRAPHICAL AND HOST DISTRIBUTION. 



After excluding these questionable records we are confronted with 

 the following facts in regard to the known distribution of the species 

 of Gyropidae. First, it is a group of a clear-cut, restricted geographi- 

 cal range ; second, it is one with a marked and restricted preference 

 as to host groups; third, at the same time also it is a group that is 

 maintaining itself in nature on distantly related mammalian orders. 

 The fact that only a veiy few of the species, as far as known, have 

 successfully established themselves on indigenous representatives of 

 distantly related orders indicates that in the phylogeny of these host 

 orders there has been a crossing over of the, ectoparasites from their 

 most favored group, the Rodentia, to the less favored ones, the Pri- 

 mates and Ungulata. That the presence of Gyropidae on Primates 

 and Ungulata is to be thus explained is further indicated by the 

 fact that the Old World Primates and Ungulata, as well as the 

 Nearctic Ungulata, are, to the best of our knowledge, without 

 Gyropid lice. If their presence is to be explained by the parallelism 

 in descent of host and parasite, certainly the neotropically exotic 

 Primates and Ungulata should also have these gyropid species; but 

 they do not harbor them, at least to the best of our knowledge. 



Would it not be hard to get a better accumulation of circum- 

 stantial evidence for the " crossing over " of a parasite group from 

 what is apparently its original and favored host group to others 

 having no phylogenetic relationship to the former? But if we 

 grant that this " crossing over " has taken place, how are we best to 

 explain it? Evidently in the case of small wingless animals the 

 first requirement for such a transfer would appear to be the coin- 

 habiting of the same area by the different nonrelated host groups. 

 This condition obtains. Next, in tlie case of ectoparasites provided 



5596— 24— Proe.N.M. vol.63 38 ^ . 



