UNIVERSITY OF CALIFORNIA PUBLICATIONS 

 ZOOLOGY 



Vol. 3, No. 1, pp. 1-12, Pis. 1 and 2 January 26, 1906 



SOME OBSERVATIONS ON THE NERVOUS 

 SYSTEM OF COPEPODA 



BY 



C. O. ESTEELY. 



The question of the innervation of the sensory hairs of Ar- 

 thropoda has long been under discussion. This may be said to 

 hold both for auditory and other sensory hairs of higher Crus- 

 tacea and Insecta and for the bristles and aesthetasks on the 

 antennae of Entomostraca. Clans ( '60) claims that a nerve 

 fibril can be traced into the appendages on the anterior antennae 

 of Cyclops, and later he establishes this for other animals. Vom 

 Rath ('87), ('88), ('91), without distinguishing sharply be- 

 tween auditory and tactile bristles, states that for every olfactory 

 and tactile (auditory) bristle there is a group of bipolar gang- 

 lion cells. Each of these cells gives off a peripheral fibre which 

 after union with similar fibres from the other cells of the same 

 group, forms a strand that enters the hair and ends only at its 

 tip. Clans ('91) agrees with vom Rath in the main but holds 

 that there is only one ganglion cell to a bristle. 



On the other hand, Retzius ('92) was unable to trace the 

 peripheral fibres farther than the base of the hair, and he found 

 several ganglion cells to each hair. Bethe ('95) states that in 

 the otocyst of Mysis there is one cell to each auditory hair, and 

 that the peripheral process extends only into the base of the hair 

 shaft. Prentiss ( :01) has shown that in the case of the otocyst 

 and tactile hairs, the terminal fibre of "the single nerve element" 

 ends in the base of the hair shaft without branching. The olfac- 

 tory/ bristles, however, receive a peripheral strand gathered from 



