LEWIS. — POLYCH^TE ANNELIDS. 261 



sense organs occurring abundantly throughout the integument of both 



worms. 



12. These sense organs show in certain regions of the body a definite 

 plan of distribution, being collected into rows, groups, and zones. 



13. Isolated sense cells are not present in the epidermis. 



14. The individual cells which make up the sense organs are bipolar 

 nerve cells, resembling the isolated sense cells which Retzius described 

 for the epidermis of Nereis. The peripheral prolongation of each cell 

 carries at its free end a single sensory hair ; the prolongation of the deep 

 end has not been completely followed out, but as far as traced is un- 

 branched; and represents a nerve fibril. 



