I76 THE PINEAL ORGAN 



which one has been more or less completely suppressed, while the other 

 has assumed a median position {vide Dendy, Gaskell, Hill, A. S. Wood- 

 ward, Stensio, and others). The demonstration of the bilateral condition 

 of the eye in an ascidian larva is thus not in itself conclusive evidence 

 of the organ not being homologous with the " parietal organ " of verte- 



oes op 



eye cl 



Fig. 128. — Salpa. A. Lateral view of section. B. Enlarged lateral view 

 of the eye and neighbouring parts (diagrammatic). 



at. : wall of atrial cavity. 

 br. : branchia. 



c. cr. : ciliated crests on the edge of 

 the branchia. 



big. : languet. 



mo. : mouth. 



n. gl. : nerve ganglion. 



ces. : oesophagus. 



ces. ap. : opening of oesophagus. 



ph. : pharynx. 



pp. b. : peripharyngeal band. 



st. : stomach. 



stol. : stolon. 



cf. : ciliated funnel. 



end. : endostyle. 



gl. : digestive gland. 



gld. : paired " neural gland." 



ht. : heart. 



int. : intestine. 



In B — br. ap. : branchial aperture ; ph. : wall of pharynx. 



(After Delage and Herouard, from Parker and Haswell.) 



brates. Moreover, the structure of the ascidian eye is more like that 

 of the parietal organ of vertebrates than that of the lateral eyes, more 

 especially with regard to the absence of inversion and the formation of 

 the lens from neural ectoderm ; but as we shall see later, these objections 

 are not insuperable when we are dealing with degenerate organs, and the 

 site of origin of the optic plate on the right side of the early ascidian larva 

 is a point in favour of Froriep's contention. 



