44 THE FLEA [OH. 



divides in the middle. The labial palpi are forced 

 apart as the mandibles and labrum penetrate into 

 the victim's flesh. Finally, they are driven entirely 

 asunder and lie flat on the skin of the host, one to 

 the right and the other to the left. The flea then 

 satisfies its hunger. A stream of blood is sucked up, 

 and when the meal is over, there is a forcible action 

 of the legs and the mandibles and upper lip are 

 withdrawn with a jerk. Numerous observers have 

 remarked on the habit possessed by fleas of dis- 

 charging the contents of their intestines whilst actually 

 engaged in sucking. In many cases a drop of bright 

 red blood is squirted from the rectum during the 

 operation of feeding, and this appears to be a common 

 practice among blood-sucking insects. Its bearing on 

 the feeding operation of the flea has not been dis- 

 covered. But its possible consequences in trans- 

 mitting diseases from host to host will be seen in 

 a subsequent chapter on fleas and the transmission 

 of plague. 



It is said that the nervous systems and brains of 

 fleas are not so highly developed as those of many 

 other insects such, for instance, as ants, bees and 

 other Hymenoptera. Having drawn attention to the 

 distinction between the external skeleton of a flea 

 and the internal skeleton of a vertebrate, one may 

 with profit do the same in the case of their nervous 

 systems. In both cases the nervous system serves to 



