2 University of California Publications. [Zoology 



as many as a liimdred cells, which "extends some distance into 

 the cavity of the hair," to end there without any modification. 



From this very brief review it will be seen that the facts con- 

 cerning the innervation of the sensory hairs of Crustacea are 

 considerably confused. The peripheral endings of the nerves of 

 the bristles and aesthetasks are not completely understood nor 

 is it known whether the manner of innervation is the same for 

 all hairs. Vom Kath holds that organs differing as widely in 

 function as auditory and tactile bristles and "sense-clubs" (aes- 

 thetasks) are innervated in the same way. 



In the present preliminary paper it is intended to report first 

 a few facts concerning the peripheral nervous system of fresh- 

 water Copepoda, and, second, an observation on the structure of 

 the central nervous system. 



This work was done partly at Harvard University and partly 

 at the University of California. It is a pleasure to acknowledge 

 the helpful direction of Prof. E. L. ]Mark of Harvard and q? 

 Prof. C. A. Kofoid of California. 



The papers of Claus ( '60), Eichard ( '91), and one by Lepe- 

 schkin ('98) are the most important ones known to the author 

 which deal specifically with the nervous system of Copepoda, 

 though Retzius ('95) and vom Rath ('91) say incidentally that 

 they have found certain facts to be true in the case of these 

 animals. Lepeschkin ('98) has used the methylene blue method 

 and reported his results but I have not seen his paper ; and Kotte 

 ( :03) states that he has obtained nerve fibre impregnations in 

 Copepods by allowing the animals to remain in a "weak solu- 

 tion" of methylene blue for several days. 



I have been able to obtain excellent staining of certain ele- 

 ments in the antennae of Diaptomus by the use of a 1/100 solu- 

 tion of methylene blue in water. The appendages have been 

 studied before and after fixation of the stain, and the results of 

 the two times agree in essential particulars. The methods of 

 fixation were the methylal method recommended by Parker ( '92) 

 and his corrosive sublimate alcohol method (Parker '97, p. 4). 

 There is little difference, if any, in the results obtained from 

 these methods. 



