40 Trans. Acad. Sci. of St. Louis. 



The list of the mites recorded from more than one host 

 species in this group is in itself extremely long, while the 

 total number of all the species is over 400. The various 

 genera and species differ greatly in their external mor- 

 phology and considerably in their internal structure, yet 

 their food habits are practically the same. 



In their distribution according to host species most 

 of the forms fall into two classes; those confined to a 

 single host and those found on several closely related 

 host species. Although over half of the known forms are 

 at present reported from only a single host, this does not 

 indicate in the least that most of these have such a re- 

 stricted host distribution ; the reason they have not been 

 reported from other hosts being that no search has been 

 made for them on other hosts, or at least no careful and 

 thorough search for them. 



In regard to the Analgesid species it will be noticed 

 that frequently there is a greater range of hosts than is 

 usually found in the mite species of other groups excepting 

 the Ixodoidea. No case, however, is known of one of these 

 forms being reported from other than a bird host, hence it 

 is probable that they could not survive upon such forms as 

 mammals. In the absence of direct inoculation experi- 

 ments upon mammals it is hard to tell just why this is. In 

 the Mallophaga, a group of more unity of structure and of 

 comparatively few individuals, a few bird-inhabiting 

 forms are found also on mammals. Since the Mallophaga 

 of the birds live upon the barbules of feathers it is easy to 

 see that one of them would find insufficient food when 

 transferred to a mammal ; but this would not be true of the 

 Analgesidae, for they live upon old epidermal scales and 

 oily secretions. As far as the diet is concerned I can not 

 see why these mites could not live upon mammals. It is 

 my opinion that the reasons are mechanical. In the flatten- 

 ing of the form of the analgesid body, it has become de- 

 pressed, not compressed, hence when turned edgeways be- 

 tween the hairs of a mammal the mite would lose its foot- 



