54 THE FLEA [CH. 



The mouth of a flea, as of any other insect, is 

 merely an orifice which forms the opening into the 

 alimentary canal. Around the orifice are the various 

 mouth-parts which convey blood to the mouth, but 

 these, the reader will doubtless remember, are the 

 modified limbs or appendages of the segments that 

 compose the flea's head. The mouth, then, gives 

 access to the digestive canal. The first part nearest 

 the mouth is the pharynx which merges gradually 

 into the gullet. Here is placed the pharyngeal pump 

 which is provided with a sucking apparatus. Muscles 

 attached to the dorsal part of the so-called aspiratory 

 pharynx cause it to expand and contract, owing to 

 the elastic reaction of its walls. The operating 

 muscles, which do this, are in the head of the flea. 

 When these pharyngeal muscles contract and relax 

 in regular sequence, a rhythmic action of the pharynx 

 itself ensues and a steady stream of blood is forced 

 or drawn from the mouth stomachwards. In a light 

 coloured flea, under a powerful lens, this action may 

 be watched in the living insect. 



Behind the pharynx comes the gullet, which leads 

 down to the gizzard, It is perhaps needless to add 

 that this organ, neither in appearance nor in use, 

 bears any resemblance to the gizzard of a bird, which 

 grinds hard food. The food of the adult flea consists 

 solely of liquid blood. 



The organ called gizzard in the flea, for want of a 



