THE HEAD OF THE BEE AND ITS APPENDAGES. 39 



organs of hearino- have been discovered on any other part of the body, 

 some of the antennal sense organs must be auditory in function. His 

 conchision from these premises is, of course, inevitable that the 

 closed sacs on the antenna^ are the hearing organs of the bee. What 

 invalidates the argument, however, is the fact that no one has yet 

 produced any actual evidence that bees perceive sound. 



The following, then, may be stated as a general sumnuiry of the 

 evidence concerning the antennal senses and their sense organs in 

 the bee: (1) The antenna> are highly sensitive to touch and are the 

 seat of the sense of smell. (2) The}' are covered by several kinds 

 of minute structures which are modified hairs containing special 

 nerve-endings. (3) By inference, it would seem certain that these 

 are the sense organs, but we can only form an opinion, based upon 

 their structure, as to which are tactile and which olfactory. (4) One 

 set of organs does not appear to belong to either of these categories 

 and their structure suggests an auditory function, but, in the absence 

 of evidence that bees hear, the purpose of these organs must be re- 

 garded as problematical. 



3. THE MANDIBLES AND THEIR GLANDS. 



The mandibles (fig. A, Md) are the dark, strongly chitinous 

 appendages of the head, commonly called the jaws, situated at each 

 side of the mouth, anterior to the base of the proboscis. In all in- 

 sects with biting mouth parts the jaws work sidewnse, each being 

 attached to the head by an anterior and a posterior articulation. 

 They can thus swing in and out on a longitudinal axis in such insects, 

 as the bee, that carry the head with the mouth directed downward, 

 or in the same way on a vertical axis in those that carry the head 

 with the mouth forward. 



Both mandibular articulations are of the ball-and-socket type, 

 although in the bee the socket is a very shallow one, the anterior 

 consisting of a condyle on the outer angle of the clypeus fitting 

 against a facet on the mandible, and the position of a facet on the 

 lower edge of the postgena receiving a condyle from the mandible. 

 The motion of the mandible is thus reduced to a hinge-joint move- 

 ment, and, on this account, insects can only bite and crush their 

 food: they can not truly chew it, since their jaws are incapable of 

 a grinding motion. Each mandible is, of course, as pointed out in 

 the introduction, really suspended from the head by a continuous 

 membrane between its base and the cranium, being simply a modified 

 saclike outgrowth of the head wall. The two articulations are pro- 

 ductions of the chitin on the outside of this membrane. 



Figure 9 A shows the location and shape of the mandibles {Md) 

 of the worker as seen in a facial view of the head. Fiafure 11 A 



