12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 7/ 



Structure of the organs of vision will be but briefly treated in this 

 paper. The protocerebral segment of the head has no true appen- 

 dages, and there are probably no muscles innervated from the 

 protocerebrum. Therefore, this part of the brain contains few 

 motor cytons. Kenyon (1896) says there are motor fibers in the 

 ocellar nerves of the honeybee, but he believes that they regulate 

 the activities of the pigment in the ocelli. 



The deutocerebrum, or second division of the brain (fig. 4, 2Br), 

 consists mostly of the large antennal lobes and the fibrous tracts of 

 the deutocerebral commissure {2Coni). The appendages of the 

 deutocerebral head segment are the antennae. These organs in 

 insects are highly sensitive structures, being provided with sense 

 receptors of many diflerent kinds. They are also delicately mobile, 

 and are responsive to subtile influences from all parts of the body. 

 Each contains muscles that move its flexible parts, while the appen- 

 dage is moved as a whole by muscles within the head inserted upon 

 its base. Each antenna is trarisversed by a nerve trunk, commonly 

 double, which contains, at least in its proximal part, both sensory 

 and motor fibers, and each trunk gives off from its base a motor 

 branch to the antennal muscles of the head. The roots of the an- 

 tennal nerves lie within the antennal lobes of the deutocerebrum. 



The motor cytons of the antennal nerve, according to Jonescu 

 (1909), in the honeybee, are arranged in two groups correspond- 

 ing with the two divisions of the nerve trunk, one group being 

 in the upper part of the antennal lobe, the other in the ventral 

 part. Kenyon (1896) says that collaterals from some of the motor 

 axons branch upon the bases of the mushroom bodies, but that 

 the majority of them go backward to the tritocerebral region of 

 the brain and to the suboesophageal ganglion, where they come in 

 contact with nerve ends from this ganglion and from the ventral 

 cord. The motor cytons thus mark the roots of the antenno-motor 

 fibers as belonging to the deutocerebrum ; but the stimuli received 

 by the fibers may come from all possible sources. 



The sensory antennal fibers end in fine branches within neuro- 

 pile bodies, or glomeruli, of the antennal lobes. These bodies con- 

 tain also the end branches of connective fiber collaterals, the prin- 

 cipal axons of which go to the mushroom bodies, in the calices of 

 which they break up into terminal aborizations. Here these fibers 

 come into close relation with the branches of the mushroom body 

 nerves themselves, and with the terminations of all the other nerves 

 that center in these bodies. The sensory stimuli received by the 

 antennae may thus be transmitted to motor nerves going out to all 



