PIGMENTATION OF THE EYES OF VERTEBRATES 69 



describes the whole triangular area shown in the figure as the " parietal 

 cornea " or " Scheitelfleck " (parietal-spot). He defines the cornea 

 as comprising all the layers between the pineal organ and the surface 

 of the head. It has a " glass-like transparency " and consists of, first, 



G.C. 



j~3s- 





RSbr. 





N.S.C. 



awn 





^tSSSbt 



G.C. 

 Fig. 45. — Parietal Sense-Organ of Geotria, the New Zealand Lamprey. 

 The Stage represented is of the Sexually Immature Form, " Velasia 

 Stage." (After Dendy.) 



Sagittal section of the right parietal eye (slightly diagrammatic) showing the 

 general structure of the organ. 



At. : atrium. 



C.T. : connective tissue. 



G.C. : ganglion cell. 



I.S.P.C. : inner segments of pigment cells. 



N.C.C. : nuclei of columnar cells of pellucida. 



N.S.C. : nuclei of sense cells. 



O.S.P.C. : outer segments of pigment cells. 



P.N. : pineal nerve. 



P. Str. : protoplasmic strands in interior of vesicle. 



Pell. : pellucida. 



Ret. : retina. 



a thin fibrous layer, continuous with the cranial wall, and, next, the eye. 

 This is convex towards the surface. Superficial to it is a conical mass of 

 transparent mucoid tissue — the " parietal plug " of Dendy (Fig. 134, 

 Chap. 17, p. 188). Over the mucoid tissue lie the corium and epidermis. 

 The branched pigmented cells of the surrounding corium are completely 



