Langdon, Sense-organs of Nereis virens. 63 



margin of the palp ganglion (see Text-figure 3). The peripheral 

 processes from the cells of one of these organs usually branch 

 several times. The ultimate ends of all of these branches come 

 together in a small area just beneath the cuticula and each, as 

 far as I have been able to make out, terminates in a little end- 

 bush. The cell-bodies and peripheral processes of these organs 

 lie in a large mass of fine, interwoven connective tissue. The 

 dorsal part of this mass is cone-shaped and the apex of this 

 cone appears to reach the cuticula and to contain the peripheral 

 ends of the peripheral processes of one of these anterior organs. 

 If this be correct, the peripheral processes of the cells in this 

 organ would have no direct connection with epidermal cells or 

 with the exterior. My sections, however, are not such as to 

 enable me to decide this point with certainty. These organs 

 were first seen by Retzius ('95) in N. diversicolor. He says 

 concerning them : "Es findet sich in den Palpen, und zwar an 

 ihrem inneren Umfange, jederseits ein eigenthiimlicher Ner- 

 venzweige welcher aus einer beschrankten Anzahl von Fasern 

 besteht, die ein grob-varikoses Aussehen darbieten und vorn 

 einen kolbenformigen Klumpen bilden. In diesem treten starke 

 Verdickungen der Nervenfasern hervor, die jedoch nicht als 

 kleine kernhaltige Nervenzellen imponiren, sondern eher das 

 Aussehen von motorischen Nervenendigungen darbieten." An 

 organ lies so close to a palp that a surface view would mislead 

 one as to its position. My sections of N. virens plainly show that, 

 in this species at least, this organ lies in the prostomium and also 

 that the "starke Verdickungen der Nervenfasern " are nerve 

 cells. It is evident that Retzius supposed these nerve-fibers to 

 be motor fibers innervating the palps. The peripheral situation 

 of the cells that give rise to these fibers, the appearance of the 

 organs as a whole, and the fact that the peripheral processes 

 appear wholly unconnected with muscles, would all tend to 

 prove that this is a true sense-organ. Of its probable function 

 I can at present only conjecture. 



I have several times seen an appearance that suggests that 

 the surface of the palp adjacent to the organ just described is 

 modified into some sensory structure. In the base of the epi- 



