xiv INTRODUCTION 



out by a study of the nearest allies of a given parasite and mem- 

 bers of a given family of parasites, in which the gradation from 

 free living animal to parasite may often be traced. Among the 

 biting lice (Mallophaga) there are species which have the power 

 of running freely, e. g. Menopon pallidum, the common hen 

 louse, which may live for a considerable length of time off its 

 host, while other species have become quite sessile, as in the case 

 of the worm-like louse Menopon titan, which inhabits the pouch 

 of the pelican. Among the fleas there are also good examples 

 of this gradation in habit and structure, e. g. the human flea, 

 Pulex irritans, while it has developed the springing power, is 

 comparatively free to move from place to place, while the hen 

 flea, Xestopsylla gallina, is quite sessile and holds fast at one 

 point to draw blood much like a tick. 



The ectoparasites will be studied first, on account of the 

 greater ease of handling them. In the meantime the student 

 will gain greater efficiency, preparatory to studying the more 

 difficult entoparasites. 



DIRECTIONS 



The student should provide himself with a hand lens and 

 loose leaf drawing paper and notebook. 



Drawings should be made with a hard pencil, preferably 3H. 

 Do not use a fountain pen or soft pencil for this work. 



Notes should be taken on each exercise and properly inter- 

 leaved. 



Each exercise will provide enough material for a laboratory 

 session of from 2^2 to 3 hours. 



Specimens, whether mounted dry, on slides or otherwise 

 prepared must be handled with care. 



Special care must be exercised in studying microscopic slides 

 under the compound microscope. Do not crush the specimen 

 by running the objective down upon it. 



