336 



could perceive light were there no pigment present, since in the fovea 

 centralis of albinos, where vision is perfect, all visual pigment ') is 

 wanting. 



Fig. 4. 



Fig. 5. 



Fie. 6. 



Fig. 7. 



Fig. 8. 



Fig. 4. Dorsal view of the ganglion and adjacent structures in S. cordiformis, chain 

 form. (30 Diam.) 



cj ciliated funnel; e eye; gg ganglion; n nerves connecting the lateral outgrowths 

 with the ganglion ; n nerve from lateral outgrowth. 



Fig. 5. Transverse section of one of the lateral outgrowths from the ganglion in 

 S. cordiformis, chain form, showing the irregular thickening of the cell walls. (340 Diam.) 



Fig. 6. Sagittal section of portions of the ganglion and dorsal eye of S. pinnata, 

 chain form ; showing, in addition to the large dorsal eye (e), one of each pair of smaller 

 eyes (e' and c"). The dorsal eye is seen to be pigmented {]p pigment) : the smaller eyes 

 are unpigmented. (575 Diam.) 



Fig. 7. Sagittal section of ganglion and dorsal eye (e) of S. costata; showing also 

 two smaller eyes (e' and c"), the former being associated with pigment cells (^'). p pig- 

 ment cells of dorsal eye. (120 Diam.) 



Fig. 8. Transverse section of the anterior part of the eye of S. cylindrica, solitary 

 form ; showing at « a cluster of rod cells far removed from any pigment cells, p pig- 

 ment; ec ectoderm, os optic sheath (ectodermal). (400 Diam.) 



1) Using the term visual pigment to include both the pigment 

 epithelium and the visual purple. 



