Ewing — Significance of Parasitism in Acarina. 13 



Debmanyssidae. — Parasitic mitea, but the habit of parasitism I3 evi- 

 dently not of very long standing, since some of the members ar« 

 yet facultative parasites, and few species show any noted symptom* 

 of degeneration. 



Gamasidae. — As far as habits are concerned this group Is very hetero- 

 geneous. Most of the species are free and predaceous; however, 

 many species live In various degrees of symbiotic relationships 

 with certain Insects, especially the ants. Some of these are pure 

 scavengers, others live upon the salivary secretions with which 

 the ants cover their eggs, while others feed upon food regurgitated 

 by the ants. At least two genera are true parasites, while semi- 

 parasitic species are found in the genera composed mostly of frea 

 species. 



Ubopodidae. — Most of the members of this group are predaceous In their 

 adult btate. In the nymphal state they are frequently found at- 

 tached to various arthropods for the purpose of transportation. A 

 few forms are parasitic when mature. 



Obibatidae. — Free-living forms. They are found In dark, moist places, 

 where they live upon fungi or small bits of decaying matter. 



NoTHBiDAE. — A large family. They are especially characterized for their 

 hard, chitlnous integument. They live under bark and under logs 

 where It is moist and feed upon small vegetable organisms and 

 rotten wood. 



HoPLODERMiDAE. — A Very small group of vegetable feeders of similar 

 habits to the preceding family. 



Pediculoidiu.\e. — The members of this family are very small and con- 

 stitute a very heterogeneous group. Some of the members are 

 plant feeders, others will make sporadic attacks upon animals, and 

 a few are real parasites. 



Tabsonemidae. — Contains two well represented genera, one of which I» 



plant feeding and one which has free as well as parasitic forma 



and Intermediate stages. 

 Ttbogltphidae. — This Is a small family In species, but large In number 



of Individuals. They are atracheate creatures, blind and live as 



scavengers. Individuals of the genus Histiostoma are taking u^) 



parasitic habits. 

 LiSTEOPHORiDAE. — Thls Is probably not a natural group, but the forma 



included in it have been so placed because of a similarity of habit. 



They are parasitic upon small mammals. 

 Analgesidae. — A very large family. They live In the plumage of birds, 



feeding upon epidermal scales, excreted matter, etc. About 400 



species are known. 

 Canestrinidae. — Only a few species represented and these are parasitic 



on insects. Hemisarcoptes is hardly a true parasite as yet. 



