2 Journal of Comparative Neurology. 



I. Introduction. 



The following work^ was begun in the Zoological Labora- 

 tory of the University of Michigan in 1 894 under the direction 

 of Prof. Jacob Reighard and has since been carried on there 

 except during the summer of 1896. At this time, the applica- 

 tion of the intra-vitam methylene blue stain to the material in 

 hand was worked out in the Marine Biological Laboratory at 

 Woods Hole under the direction of Prof. A. D. Morrill of 

 Hamilton College. 



With the exception of the four eyes, none of the sense-or- 

 gans of Nereis virens have previously been described, though 

 paired cephalic sense-organs of unknown function and isolated 

 epidermal sensory cells have been described in other species of 

 this genus and the latter have been briefly mentioned for N. 

 virens itself. The following account contains a detailed de- 

 scription of two kinds of sense-organs — diffuse sense-organs and 

 spiral organs — which are found scattered over the body in the 

 epidermis of this worm, and also a brief description of two 

 pairs of organs which are found in the prostomium. The diffuse 

 sense-organs are simple epidermal organs which are directly 

 comparable with the epidermal tactile organs of the Oligo- 

 chaeta. Isolated sensory cells, which are similar to the cells of 

 the organs described in this paper and may prove to be identi- 

 cal with them, have been described for other species of Nereis; 

 the diffuse sense-organs themselves have never been described 

 for Nereis but have recently been described for two other gen- 

 era of the Polychaeta — Axiothea and Clymene. The spiral 

 organs are complicated organs whose structure differs consid- 

 erably from that of any organ previously described. They 

 are, however, so nearly like the epidermal ocular organs of va- 

 rious invertebrates, that they may be considered to have for 

 their function the perception of light. The two pairs of ceph- 

 alic organs are of problematical function and have been already 

 found in other Polychaeta. 



A brief abstract appeared in Science, Vol. V, p. 427 {1897). 



