PINEAL EYE IN LACERTILIA. 207 



In both, the cells are seen to be much elongated with very dis- 

 tinct nuclei ; in the case of the anterior ones, save for the 

 presence of well-marked cilia, they differ but little from those 

 of a lens. An elongation of those lying in the middle would, 

 in fact, transform this into the lens of such a form as Lacerta 

 ocellata (PL XVIII, fig. 30). 



Passing to the posterior surface, however, a curious but 

 interesting modification takes place (cf. figs. 19 and 20), the 

 nuclei all pass to the external surface, whilst the 

 ends of the cells, which are left facing into the cavity 

 of the vesicle, bear a close resemblance to the rod- 

 like structures of the retina of other forms. 



It is possible that we have here a stage in the development 

 of the retina. The internal portion of the cell forms the 

 '^ rod,^' the nucleus passes to the external end, and with the 

 protoplasm lying around it forms the spherical- shaped element 

 of the retina, still retaining its connection with the rod. Other 

 cells, lying on the opposite side (supposing the wall of the 

 vesicle, as in Cy clod us, to be more than one cell thick), 

 become transformed into the external-lying elements of the 

 retina, their protoplasm becoming in part drawn out into pro- 

 cesses, which enter into connection with those of other cells, 

 in part remaining arouod the nuclei, forming thus the external 

 spherical elements and the processes connecting these with each 

 other. This development would give exactly such a structure 

 as has been already described in Varanus giganteus. In 

 this form it is noticeable that the spherical elements of the 

 retina consist of nuclei with a small amount of protoplasm 

 around them, the nuclei being identical in size with those of 

 the lens, the greater part of the protoplasm of the cells seeming 

 to be developed into processes connecting the various elements. 

 By this means is developed a network of branched cells, con- 

 nected on the one hand with rods, and on the other with nerve- 

 fibres. 



In Cyclodus the stage is reached and retained in which the 

 rods have begun to be formed by a removal of the nuclei to 

 the outer ends of the cells, where they form, together with 



