1910.] and Adjacent Parts of the Brain in the Tuatara. 635 



specially differentiated, and project as small rounded protuberances into the 

 cavity of the eye. The nuclei are situated at various levels, and the 

 cytoplasm of the inner portions of the cells is very distinctly fibrillated in 

 a longitudinal direction, while darkly staining bodies resembling centrosomes 

 can sometimes be seen close to the inner extremities of the cells. 



In the adult lens, about the middle, one usually, if not always, finds one 

 or more irregular masses of a finely granular, deeply staining substance. It 

 was the observation of a large mass of this kind, with a centrally placed 

 nucleus, which led to my description of a " central cell " in the lens, and it 

 was chiefly with a view to further investigation of this remarkable structure 

 that this research was undertaken. I now find that such central masses 

 are very constant features of the adult lens, and their true nature was 

 indicated by the fortunate occurrence of an adult specimen in which such a 

 mass was actually being extruded in the form of " mucus " into the cavity 

 of the eye to take part in the formation of the vitreous body. I have 

 observed this extrusion of " mucus " into the cavity of the eye in several 

 cases, and as early as stage K. With the " mucus," nuclei may pass out 

 from the lens, and there can be no doubt that the secretion is formed by 

 degeneration of cells in the middle of the lens. The extrusion always 

 appears to take place from the middle of the lower surface of the lens at a 

 very definite spot, but an actual aperture is probably present only at the 

 time when the secretion is being poured out. 



The vitreous body always contains, in preparations, a reticulum of slender 

 fibres or thin lamellae, and some of these are attached, on the one hand, to 

 the inner surface of the lens, and, on the other, to the inner surface of the 

 retina, apparently in many cases to the projecting ends of the sense-cells, 

 but probably really to the caps which cover these. Whether the presence 

 of this reticulum is due to post-mortem changes or not remains an open 

 question. 



A large amount of time has been devoted to following out the course of 

 the nerve of the pineal eye, and I have been able to demonstrate very 

 clearly that it is not a median structure, but belongs to the left side of the 

 body — another striking piece of evidence in favour of the paired origin of 

 the pineal organs. 



In the adult animal the anterior end of the nerve, like the eye itself, has 

 been shifted into the middle line. For the greater part of its course, 

 however, it lies between the wall of the pineal sac and the wall of the dorsal 

 sac, and considerably to the left side of the middle line. It is very easy to 

 follow it from the eye towards the brain up to a certain point, where it breaks 

 up into a number of separate strands. This point lies between the posterior 



