Vol. 3] Esterhj. — Nervous System of Copepoda. 5 



seen in the fnreal bristles of Diaptomus, but one should reserve 

 a positive declaration that there is no such thing in that case. 



It has been possible to detect a nerve supply for the rostral 

 filaments of Diaptomus in my preparations with methylene blue 

 (PI. 2, figs. 12, 13, 14). The function of the filaments has been 

 problematical though Claus looked upon them as protective 

 organs. The presence of innervation would seem to indicate that 

 they are sensory in function. I have seen in a good many cases 

 that a nerve fibre passes from a ganglion cell to each prong of 

 the rostrum, there to ramify much as in the ease of aesthetasks 

 of the antennae. In most cases I have seen but one such cell for 

 each filament, and cannot give it its central connection, though 

 it can be said with accuracy that there is one ganglion cell for 

 each rostral filament. Figs. 12, 13, and 14 show the appearance 

 in side view and fig. 14 gives the location of the cell Avell enough 

 for our present purpose. In one case it was very clear that the 

 peripheral processes of two ganglion cells united and then passed 

 to one prong of the rostrum. 



The structure of the central nervous system to be mentioned 

 briefly is shown in PL 1, figs. 9, 10. This has been observed 

 several times in both male and female animals. It will be seen 

 in fig. 10 that the two cells located in the last segments of the 

 abdomen give ot¥ anterior and posterior processes. The former 

 unite and the single fibre thus formed has been traced forward 

 as far as the level of the second maxillipecl. Nothing more as to 

 its structure or connections can be said at this time, though it 

 is probable that it belongs in the category of fibres described by 

 Richard ('91, p. 205, figured on PI. 8, figs. 6, 7, or 31). What 

 connection it has with the condition he shows in PI. 7, fig. 4, I 

 cannot say. 



SUMMARY. 



1. Each aesthetask-bearing joint of the anterior antennae of 

 the male and female of Diaptomus contains a group of cells which 

 stain with methylene blue. It can be seen that peripheral pro- 

 cesses arise from such cells and unite into a single strand to 

 enter the aesthetask. 



