PINEAL EYE IN LACERTILIA. 225 



tilia as descendants of some common ancestor, we can come 

 to no other conclusion, inasmuch as the more primitive and 

 specialised forms agree at the present time in the possession of 

 a parietal foramen occupied by a pineal eye, and that this is, 

 further, a characteristic of the nearest allies of the forms 

 mentioned, than that the ancestral form possessed both these 

 structures, and that the condition seen in Chameleo, Cy- 

 clodus, and Lyriocephalus is not typical but secondary; 

 they possess a parietal foramen simply because their ancestors 

 possessed a pineal eye, which in them is in a rudimentary con- 

 dition, as indeed the external modification in Cyclodus 

 (PI. XV, fig. 9) seems to show in the case of this form in 

 particular. 



When, therefore, we find the parietal foramen exceedingly 

 well developed throughout all the group Labyrinthodonta, 

 we are justified in concluding that in them a pineal eye 

 was in all probability present, even though we may grant 

 the possibility (an unlikely one under the circumstances) of its 

 occasional presence, as in Lacer tilia, in a low state of 

 development. 



In living Reptilia the presence of the foramen is confined 

 to one group, but amongst the extinct forms, which may be 

 regarded as the ancestors of the Reptilia now living, whilst 

 some, at all events, may further be regarded as intimately 

 connected with the ancestors of living birds, we find that the 

 foramen is a well-developed structure. Judging from its 

 present condition in the relatively small Lacertilia of the 

 present day, we may imagine that in the huge extinct forms of 

 Mesozoic periods — in such as Ichthyosaurus and Plesio- 

 saurus, the walls of whose foramina even present rugosities 

 as if for the insertion of muscles — the pineal eye attained a 

 development and importance quite disproportionate to that 

 with which we are now acquainted in any living form.^ 



^ I am indebted to Professor Moseley for calling my attention to the paper 

 upon " The Brain of a Theromorphous Reptile of the Permian Epoch," by Cope, 

 in which is figured a cast of the brain of one of the Diadectidae. Perhaps 

 the most remarkable feature is the huge comparative size of the cavity within 



