64 Journal of Comparative Neurology. 



dermis of a small area are a number of apparently isolated, 

 spindle-shaped, bipolar nerve-cells. The peripheral process of 

 each cell appears to pass in a small canal through the cuticula 

 and to project above the surface as a sensory hair. The central 

 processes from these cells join each other to form small nerves 

 which later unite and pass to the brain. If this observation 

 should be verified, there would be proved to be on the base of 

 the inner side of each palp a small sensory area thickly covered 

 with cilia which are born by nerve cells apparently identically 

 like the component cells of the diffuse sense-organs. 



Each of \)[i& posterior pair of cephalic oj-gans lies on the an- 

 terior surface of a little pocket-like invagination which is situ- 

 ated between the prostomium and peristome just caudo-laterad 

 and somewhat ventrad of the posterior eyes (Plate II, Fig. 28). 

 Retzius ('95) has briefly described these organs in Nereis diver- 

 sicolor ; Racovitza ('96) has made a somewhat extended study 

 of them — he calls them "Organe nucae" — in Nereis dumerili 

 and in many other Polychaetes. Hamaker ('98) has given a par- 

 tial description of them in N, virens itself. These organs in Nere- 

 is virens are practically the same as those described for the two 

 species studied by Racovitza. Each is an elongated area of very 

 long epidermal cells among whose peripheral ends lie the free 

 terminations of the peripheral processes from a group of 

 bipolar nerve-cells situated in the posterior brain. I have, 

 however, found among the central ends of the epidermal cells 

 of this area the wandering cells bearing yellow pigment which 

 Racovitza has described in other genera but not in Nereis. I 

 have not been able to see that the final ends of the central fibers 

 from the nerve-cells end in fine branches as described by Ret- 

 zius nor that the epidermal cells bear cilia as described by 

 Racovitza and Hamaker. My failure to observe the latter is, I 

 am sure, due to my material, not to the absence of these cilia. 

 Racovitza states that these organs are difficult to see in the 

 living animal because "ils sont caches sous un repli du bord 

 anterieur du premier segment," a view also held by Hamaker. 

 It is, however, more than these folds which conceals these or- 

 gans. Each is really situated on the anterior surface of a pocket- 



