Vol. 3] Esterly. — Nervous System of Copepoda. 3 



It is known, chiefly from the publications of Schmeil ("96), 

 that certain of the joints of the anterior antennae bear the modi- 

 fied sensory bristles or aesthetasks (sense-clubs, Riechschlau- 

 chen). In my methylene blue preparations it can be seen that in 

 each joint which carries an aesthetask there is a group of cells, 

 each cell givine: off a peripheral fibre which unites with those of 

 the other cells to form a single strand (PI. 1, fig. 1). This enters 

 the sense-club where it terminates in fine fibrils (PI. 1, fig. 5). 

 These do not seem to lie free in the interior of the club, but upon 

 its extremely delicate walls. 



The number of cells in the groups varies somewhat, but there 

 are always more than one, and seven is the largest number seen 

 in one group. The groups of cells always lie in the seginent 

 carrying the aesthetask M'hich they innervate, and they are 

 always proximal to the sense organ ; that is, the strand formed 

 by the union of the peripheral processes of the cells passes to- 

 ward the distal end of the antenna to enter the sense-club. 



Little more can be said at present as to the structure of the 

 ending within the aesthetask than that in the majority of cases,. 

 both before and after fixation, there is a heavily staining globule 

 just at the point where the sense organ begins to broaden out 

 from the narrow stalk-like basal portion (PL 1, figs. 2, 5). Be- 

 yond this body the terminations seem to be of the ordinary fibril- 

 lar type. There is some evidence, based on staining reactions, 

 that there are tw^o sorts of cells in the group. This appears both 

 in fresh and fixed preparations. Some cells stain more lightly 

 than others, but both send processes to the sense organ (PI. 1, 

 figs. 1, 6, 8). There is an indication that one sort of cell is 

 unipolar, the other bipolar ; but evidence on this point is scanty 

 and the matter is merely mentioned here. There is no doubt 

 that bipolar cells enter into the group. 



Hundreds of preparations have been seen in which each aes- 

 thetask-bearing joint of both antennae in each sex contained a 

 group of cells as described above. Many cases have been care- 

 fully examined under high power, and without exception the 

 conditions of the innervation of the sense organs are as described. 

 Not all of the sense organs on the grasping antenna of the male 



