16 Trans. Acad. Sci. of St. Louis. 



most as well adapted for sucking the blood of animals as 

 the juices of plants. Mr. Tucker^ has recently made some 

 careful observations on several species of plant-bugs in 

 regard to their attacks on man. He found that several 

 of these, particularly some of the Jassidae, or leafhop- 

 pers, would at times attack human beings and cause them 

 much annoyance. In doing so they really did feed on 

 the blood of the individuals bitten. In regard to the 

 attacks of Empoasca mall Le B. he states: "From the 

 time my attention was first attracted by feeling the bite 

 until the insect desisted, a trifle over four minutes 

 elapsed according to my watch. The first insect was then 

 captured, and after being crushed on a white sheet of 

 paper a faint bloody streak was produced, which proved 

 beyond any doubt that the specimen had actually en- 

 gorged itself with blood." 



In the Acarina we find the parasitic liabit developed 

 independently from several groups of free-living forms, 

 but in each case I think that its method of development 

 has been over one of the three roads indicated above. 

 By a study of Table I the following classification of the 

 free-living Acarina can be made, all of them falling into 

 one of three classes. These classes are as follows: 



I. Free-living predaceous forms: usually provided 

 with eyes and prehensile organs; possessing a delicate 

 sense of touch and being very agile in movements. To 

 this class belong: 



The Eupodidae and Bdellldae. 



Caeculidae (Habits doubtful but probably predaceous). 



Of the Cheyletidae, the genus Cheyletus. 



Some of the Halacaridae. 



Most of the Gamasidae. 



Many of the Uropodidae. 



II. The free-living scavengers. These forms, as a 

 rule, are less highly specialized than the predaceous 

 forms (a correlation with their mode of life). They 



^ Tucker, E. S. Random Notes on Entomological Field Work. Can. 

 Ent. 43:29-31. 1911. 



