48 THE FLEA [CH. 



ears ; though it may be that they are also auditory 

 organs. They are certainly tactile and olfactory 

 organs as well. In outward structure each antenna 

 consists of two parts which may be called the stalk 

 and the club. The club is divided into a number of 

 segments and is plentifully supplied with hairs. In 

 some species the cuts which divide the different 

 segments appear to be confined to one side of the 

 club. In others a sort of central core holds the 

 segments of the club together. The antennae, there- 

 fore, are undoubtedly exceedingly complex organs. 

 Such an insect as a flea may well be far more sensitive 

 to movements of the air, vibrations of the earth, 

 smells, light rays and sound-waves than a human 

 being. In their origin the antennae, like the paired 

 mouth-parts, are modified appendages of the fused 

 segments which compose the head of the insect. The 

 fact that there are four pairs of appendages on the 

 insect's head, viz. (1) antennae, (2) maxillae, (3) labial 

 palpi and (4) mandibles has been put forward by 

 some entomologists as evidence that the head is 

 formed of four primary segments. 



Antennae apparently enable fleas to find their 

 bearings, to communicate with one another and to 

 discover the whereabouts of the opposite sex. But 

 it is especially as organs of smell that they play 

 a most important part in the flea's social life. They 

 enable couples to find one another; and, when the 



