70 Journal of Comparative Neurology. 



4. From the central end of each organ, a second bundle 

 of nerve-fibers — the central processes of the nerve-cells — passes 

 into the central nervous system or into peripheral ganglia con- 

 nected with the latter and seem to form pericellular nerve-bas- 

 kets around the ganglion cells there present. 



5. The diffuse sense-organs are most numerous in those 

 regions of the body that are most exposed to contact. 



6. It is probable that these organs serve for the percep- 

 tion of chemical and mechanical stimuli. Similar organs which 

 exist in the epithelium lining the buccal cavity probably serve 

 as gustatory organs. 



//. The Spiral Organs. 



1. The epidermis of the gill-lobes, of the enlarged bases 

 of the palps and cephalic cirri, and of about the first twenty 

 metameres of Nereis virens contains complicated organs which 

 probably form a second system of sense organs. 



2. Each of these spiral organs consist of about 100 bi- 

 or multipolar cells — apparently nerve-cells — whose peripheral 

 processes are arranged spirally around a central tube — a tube 

 apparently formed of invaginated cuticula. 



3. The bodies of the cells composing the spiral organs 

 lie in the base of the epidermis or in special pouches which pro- 

 ject centrally from this base. 



4. The peripheral processes are club-shaped and the tip 

 of each contains a refractive body. The terminal halves of these 

 refractive bodies are so arranged as to form a spiral band around 

 the central tube. 



5. The central processes have been traced only a short 

 distance centrally ; it can be seen that they pass toward and 

 almost into the epidermal nerves. 



6. The spiral organs are most numerous on those por- 

 tions of the body which are likely to be most directly exposed 

 to the light. 



7. They resemble the epidermal eyes of Invertebrates 

 and some of the simpler true eyes of the Polychaetes ; their 

 function is probably the perception of difference in intensity of 

 light. 



