42 Journal of Comparative Neurology. 



the latter would be, therefore, just as quickly perceived if the external 

 ends of these organs were more or less sunken beneath the surface, and 

 the sensory hairs themselves would be thus better protected from injury. 

 Nereis, as is well known possesses special tactile appendages which 

 probably serve for all cases in which tactile impressions are to be re- 

 ceived through actual contact with foreign bodies ; the cuticular area 

 over a sense-organ in these appendages resembles that over a sense-or- 

 gan of Lumbncus. 



The differences between the "diffuse sense-organs" of Nereis 

 and the "epidermal sense-organs" of Axiothea and Clymene are 

 as follows : In Axiothea and Clymene, the sense-organs as a rule 

 "vary in size directly with the thicknes of the cuticula;" the 

 opposite is true in Nereis. A longitudinal section of the cu- 

 ticular cavity over the sense-organs of the first named forms re- 

 sembles more that found in the appendages of Nereis than that found 

 in the body-wall, in that the inner cuticular cavity is shallow and wide 

 at its inner end and the base of the outer cuticular cavity is elevated. 

 As Lewis does not figure the two layers of the cuticula it is impossible 

 to decide whether, as in Nereis, the perforated membrane is formed 

 from the inner cuticular layer. In Axiothea and Clymene there is 

 never but one sense-hair to a peripheral process ; in Nereis there are 

 sometimes two or three. Lewis considers these hairs probably normally 

 retractile but states that she can give us no proof. She found two sensory 

 hairs stained by the blue which seemed to move for a considerable time 

 and change their position with reference to each other. This, it seems 

 to me, was due to post-mortem changes taking place in the per- 

 ipheral processes on- which these hairs were born and not to any nor- 

 mal movement. She examined the removed cuticula of Nereis and 

 concluded, from the likeness of the surface views of the cuticular areas 

 over the sense-organs to those found over the sense-organs of Axiothea 

 and Clymene that similar organs must exist in Nereis. 



Blochmann ('95) and Zernecke ('95) have described and figured 

 in the Cestodes and Blochmann and Bettendorf ('96) in the Tre- 

 matodes a peripheral sensory system of isolated bi-polar nerve- 

 cells lying partly in and partly beneath the sub-cuticular region. 

 The peripheral processes of these cells are described as entering 

 a " birnformigen Hohlraum " in the inner side of the cuticula and 

 ending in this blind cavity in a "nagelkopfahnUche Platte" from 

 which occasionally a small "Stiftchen" passes a little farther into the cuti- 

 cula. Blochmann and Bettendorf regard this "Stiftchen" as probably 

 always present but generally uncolored. Zernecke believes that, in the 



