iQio] California Rodent Fleas 65 



unless disturbed or unless the host snaps at them or scratches 

 when unusually annoyed. They hop freely when jumping from 

 the animal to the ground or vice versa, or from one host to another. 

 When a flea is cornered, that is, when it experiences difficulty in 

 passing an obstruction, it proceeds Hke a swimmer using the side 

 stroke. The parasite drops to its side and locomotion ensues by a 

 vigorous sweeping movement of the legs, almost entirely by the 

 use of the hairs and spines, especially through the medium of the 

 powerful spines of the tibia, when it ambles along on the flat 

 side in a striking manner. The spines of the leg seem to be 

 peculiarly adapted for this side motion: it is in this fashion 

 that the nimble parasite manages to become so very elusive. We 

 refer especially to the P. irritans. This may be tested by 

 holding a live flea between the thumb and forefinger and unless 

 you chance to be a flea trapper of long and painful experience 

 the ingenious parasite will surely escape. 



CONSIDERATION OF COLOR ATTRACTION. 



We have a little experimental evidence on the question of attrac- 

 tion of these insects towards color in animals. It is the prevailing 

 opinion that white animals attract the greatest number of fleas. 

 We have to report a few tests of color attraction. The material 

 used in the first experiment was six guinea pigs showing extreme 

 variations of color: three of these were pure white and three 

 pronouncedly dark. These were placed in a large cage, the 

 bedding of which was infested with squirrel fleas. After forty- 

 eight hours the guinea pigs were removed simultaneously and a 

 census of the fleas on the individual animals was made immediate- 

 ly. Fleas and animals were anaesthetized at the same time, the 

 white guinea pigs yielding respectively ten fleas, five fleas, and 

 eleven fleas. The black guinea pigs yielded eleven, seven and 

 four fleas; the last number came from a mixed black and white 

 guinea pig. A summary of the fleas from the three white guinea 

 pigs gave twenty-six fleas, or an average of about nine each ; the 

 two dark guinea gigs giving eighteen, averaging nine each, and 

 the black and white giving four fleas, all of which were of the 

 species, C. acutus, the squirrel flea. 



A second experiment was as follows: Four guinea pigs 

 were placed in a large container, which was swarming w4th squir- 

 rel fleas. After three days the animals were removed as before, 

 and a census of the parasites was taken: one brown and black 



