CONCERNING FLEAS. 143 



Three or four species of flea occur on bats, and belong to a difEerent genus 

 {^Typhlopsylla\ in which the eyes are absent or quite small ; the body is 

 relatively longer, as the abdomen is not so deep from above downwards. Mice 

 rats and shrews are attacked by three other species of this same genus, 



A third genus is found for the mole's flea {Hystrieopsylla ohtusiceps) which is 

 the largest of our native fleas, measuring 3'5 mm. to 5' 5 mm. The body is 

 particularly hairy, the head is short and rounded, and like the preceding genus 

 is without eyes. This flea is also found in the nests of bumble bees, where no 

 doubt it is a harmless visitor, having left the mole during the latter's excursion 

 through the soil.^ 



It appears then that certain species of flea are associated, not with species of 

 mammals, but with larger groups. 



It is a curious- and interesting fact, as far as we are aware, no flea has been 

 recorded as occurring in monkeys in a state of nature. Judging from their 

 actions in captivity, one would assume the presence of these parasites in con- 

 siderable numbers. A well-known naturalist informs us that he kept a monkey 

 for three years and never found a flea on it. Nevertheless, nothing seemed to 

 amuse the monkey better than for its owner to pretend to catch fleas on its coat 

 and to present them to it to be eaten. Man, therefore, does not seem to have 

 inherited fleas from his Simian ancestors ; it appears probable that he had 

 '* caught" fleas from his associates, the cat and the dog, and that the present 

 human flea, P. irritans, is descended from the same ancestor as P. serraticeps. 



The flea is really only an occasional parasite, merely visiting its host to obtain 

 food in the same kind of way that the leech merely sucks the blood of man and 

 then drops off. The flea and the leech belong to quite a different category of 

 parasites from the tape-worm or the tick, which take up their position once 

 and for all. In fact, the flea makes use of men and other animals merely as a 

 larder or provision store, and leaves its host readily. The character of the 

 blood and the thickness of the skin no doubt determines that one species of 

 flea attacks man, another the dog, and so on. On the death of its host the fleas 

 leave at once. 



The flea is fairly long lived for an insect. We have a record of one which 

 lived for 23 months in captivity, when it died of old age, 



(^The above appeared in the British Medical Journal on 5tJi January, 1895,) 



2 No doubt the other species of fleas, such as those which have been recorded from the fox, 

 jreasel, stoat, and other animals, as occurring in Germany, Holland, 'may be added to our 

 list of British forms. 



