70 Trans. Acad. Sci. of St. Louis. 



Plate VI. — A Symbion and Commensals. — Fig. 22. Macrocheles 

 moestus Banks. One of the several species of Gamasidae which live 

 in symbiotic relationship with ants. This species has been studied 

 by Prof. S. A. Forbes, who found that the ants paid much attention 

 to it and would carry these mites about as if they were their own 

 young. The mite probably lives as a scavenger of the domicile. In 

 many cases these gamasids will attach themselves to the bodies of 

 the ants and live upon food regurgitated by their hosts. — Fig. 23. 

 Pterodectes vinticus Banks. One of the commensals belonging to the 

 Analgesidae. The members of this genus live among the feathers 

 of birds where they eat cast epidermal cells and oily secretions. — Fig. 

 24 and 25. Female and male respectively of Analges passerinus 

 Linnaeus. Like the preceding species this species lives among the 

 feathers of birds upon excretory products and dead cells. 



Plate VII. — Some types of True Parasites. — Fig. 26. Psoroptes 

 cuniculi (Delaf.). Male and female in copulation. The species of 

 this genus infest the skin of mammals where they cause great slough- 

 ing of the same. They live on the cellular tissues. — Fig. 27. Micro- 

 tromhidium muscarum (Riley). It is a larval parasite of one of the 

 harvest mites. The common house fly is its true host from which it 

 sucks the blood. At times these larvae attack man himself and cause 

 intense itching. — Fig. 28. Larva of RhynclwlopJiiis. It lives as a 

 haematophagus parasite upon species of Empoasea. — Fig. 29. Eriophyes 

 ulmi (Garman). One of the gall mites. The gall mites live upon 

 the juices of plants. Often their attacks cause various malformations 

 to appear upon the leaves, some of which are called galls. The vermi- 

 form shape of the body is an adaptation similar to that of the hair 

 follicle mites. 



Issued June 18, 1912. 



