134 MANUAL OF ANIMAL BIOLOGY 



cells which, in turn, are connected by nerve fibers to the central 

 nervous system. These sensory hairs are present in great numbers 

 near the tip of each antenna. 



(2) Organs of Taste and Smell. Although the experimental evi- 

 dence is not conclusive, it is generally held that the senses of taste 

 and smell are located in tiny surface depressions, or pits, known as 

 the sense pores, which are present on the base of each antenna, 

 on the mandibles, and on various head regions. Sense organs of 

 this same structural type and which presumably function in the 

 same way are also found on the legs, the bases of the wings, and 

 the sting. Each of these depressions is connected with the central 

 nervous system by a nerve fiber which begins in a special sensory 

 area at the base of the cavity. 



(3) Other Sense Organs on the Antennae. It is known that there 

 are at least seven different kinds of sensory end organs localized 

 on each antenna of the Bee. It is clearly apparent therefore 

 that various types of external stimuli must be received by these 

 end organs. Of one kind of end organ alone, the sense plate, 

 there are about 2500 on the antennae of the queen, 5000 on the 

 worker, and 30,000 on the drone ; while the total number of sen- 

 sory nerve cells present in one antenna of the drone has been 

 estimated at 500,000. It is, of course, a very difficult problem to 

 determine the exact location on the antennae of any particular 

 sense reaction. 



(4) Organs of Sight. The Bee possesses two large compound 

 eyes, one on either side of the head, and three simple eyes, or 

 ocelli, which are situated on the dorsal wall of the head, close to 

 the median line. The compound eyes are similar in structure to 

 those found in other Arthropoda. Each eye is made up of several 

 thousand independent visual units, the ommatidia. Projecting 

 from the surface of the compound eyes, and arising from between 

 the ommatidia, are a large number of hairs which apparently are 

 protective in function. Pollen grains and other debris, which 

 lodge between the hairs, are removed by the eye brushes on the 

 prothoracic legs, the structure of which has already been noted. 

 The ocelli are regarded as simple eyes because each consists of one 

 visual unit which is believed to be similar in function to a single 

 ommatidium of the compound eye. Both the compound eyes and 

 the ocelli are innervated by nerves connecting with the cerebral 

 ganglion. 



