THE COMMON FLEA 257 



stomach, big enough to hold a large draught of blood, 

 such as the insect is only too eager to suck in whenever 

 it can get the opportunity. At the junction of the 

 stomach with the intestine are four long, thin, blind 

 tubes, the Malpighian tubules. The hinder end of the 

 intestine expands into an inverted, pear-shaped cavity, 

 the rectum, on the walls of which are six oval glands. 



The alimentary canal, when gorged with blood, can be 

 rapidly emptied by the insect, and its contents ejected 

 with considerable force, when a new and good supply of 

 food presents itself before the last meal is disposed of. 

 The dark stains on linen, that indicate where fleas have 

 been, consist of their dried excrement, and are composed 

 of the undigested remains of the blood corpuscles con- 

 tained in the food. Judging from the fact that rooms 

 that have long been unoccupied are sometimes found to 

 be swarming with fleas, it would seem that the perfect 

 insects can subsist for a time without their customary 

 food, although they are rapacious and insatiable enough 

 when it is obtainable. And even under ordinary cir- 

 cumstances, their living must not unfrequently be pre- 

 carious, and their meals most irregular. As is well 

 known, it is not every human being that they regard as 

 fit to supply them with nutriment; some individuals 

 they seem instinctively to avoid, whether by reason of a 

 greater thickness and toughness of skin, or of something 

 distasteful in the blood, or from some other cause, it is 

 impossible to say. That they should prefer a host with 

 a soft and delicate skin is only natural, and is evidenced 

 by their marked partiality for females and young chil- 

 dren, though it must not be forgotten that some of 

 this apparent partiality may be due to the extra facilities 

 that are afforded to the parasites, in the case of these 

 sections of the community, by the character of the 



