54 Journal of Comparative Neurology. 



in a 'given region always exist in the two sides of the same 

 worm and probably in the same side of different worms. 



A study was also made of the distribution of these organs 

 by means of surface views of the epidermis. As the results 

 thus obtained did not appear to be strictly accurate they were 

 not included in the chart. This study, however, tended to 

 show that the median zone of spiral organs occurred in the 

 dorsal surface of every metamere as far back as the twentieth 

 and that the number of organs in each zone back of the first 

 became gradually less. 



From a study of living parapodia it was found that the 

 spiral organs are found in the tips of each gill-lobe of every 

 parapodium ; the number found in a given parapodium depends 

 directly upon the size of the latter. As many as 15 are some- 

 times found in a single gill-lobe. 



C. Ftmction of Spiral Orga?is. 



The spiral organs of Nereis suggest three different classes 

 of organs — compound glands, phosphorescent organs whose 

 structure is similar to ocular organs, and ocular organs them- 

 selves. 



The component cells of these spiral organs not only differ 

 in structure from the isolated gland-cells in the epidermis of 

 Nereis virens, but also when tested by a special stain like Bion- 

 di-Ehrlich never take the stain of gland-cells. They always 

 stain more like undoubted nerve-elements. Moreover the most 

 careful study under the oil-immersion has failed to reveal any 

 secretion in the central tube or any opening from a peripheral 

 process into this tube. A refractive body always fills the tip 

 of each process. Sometimes the secretion from one of the 

 mucous gland cells hardens under the influence of reagents 

 in the peripheral end of the cell. But such a hardened gland- 

 ular secretion always takes an intense stain, while the refractive 

 bodies of the spiral organ remain almost if not quite colorless. 

 Moreover they are found to be hardened structures even in the 

 living condition. As far as present observations go I therefore 



