1910.] a)id Adjacent Parts of tlie Brain in the Tuatara. 637 



•elicits, so far as 1 have been able to make out, no response ; but then it 

 must be remembered that the animals are extremely sluggish, and a similar 

 ■experiment with the lateral eye may be continued for some time without 

 producing any visible effect beyond the contraction of the iris. 



Structurally, the only sign of degeneration which the pineal eye exhibits 

 is to be found in the very large amount of pigment present in it in the adult, 

 for I do not think we need regard the degeneration of the central lens-cells 

 into the mucus which helps to form the vitreous body as of any significance 

 in this respect. 



Eigenmann has shown that a great deal of pigment is developed in 

 association with the degenerating lateral eyes of the blind fishes, Lucifuga 

 and Amblyopsis, but the degeneration of the pineal eye of Sphenodon does 

 not approacli in degree that of the lateral eyes of these types, and there 

 seems no reason why it should not still function as a light-percipient organ. 

 The formation of images by the lens is, of course, out of the question, on 

 account of the irregular arrangement of the small scales which overlie the 

 parietal foramen. I find from direct experiment, however, that light can 

 pass through the integument at this point, and also through the more or less 

 transparent parietal plug which covers the pineal eye in the foramen. 



Reissner's fibre and the sub-commissural organ (" ependymal groove ") 

 are well developed in Sphenodon, and appear to have the usual relations. 

 The latter has the form of a deep groove, lined by the characteristic greatly 

 •elongated columnar epithelial cells, and extending forwards from near the 

 hinder end of the posterior commissure, beneath the latter, to the infra- 

 pineal recess. Reissner's fibre is already conspicuous at stage S. 



