100 THE PINEAL ORGAN 



greatly elongated, and are differentiated into sensory cells and pigment 

 cells. The outer ends of the sensory cells are expanded by a refractile 

 vase-shaped inclusion, the " crystal cone." The inner end contains an 



n.gr 



.n.tr. 

 ,J.p.e. 



^V-l.anL 

 » •V— X— r.a.e. 



V-oe.co. 



, per. st. 



C E 



Fig. 64. — Eyes of Polychtete Worms, showing Variations in the Number 



of Ocelli. 

 A, B- Lateral and dorsal views of the brain and eyes of Ophelia cluthensis. (After 



R. S. Brown.) 

 C, D, E — Heads of Polynoid, Eunice, and Nephthys (Cambr. Nat. Hist.). In the 



species Ophelia cluthensis the right member of the posterior pair of ocelli 



is absent. In Eunice only one pair is present, and in Nephthys the eyes are 



absent. 



br. : brain. n. tr. : nuchal lobe. 



c. : cirri. ce. co. : oesophageal commissure. 



c. 2 : cirrus of first body segment. p. : palp. 



el. : point of attachment of elytron, per. st. : peristomium. 



l.a.e. : left anterior eye. pr. st. : prostomium. 



/. ant. : lobus anterior. r.a.e. : right anterior eye. 



l.p.e. : left posterior eye. t. : tentacle. 



n. gr. : nuchal groove. 



