2 9 S SCIENCE PROGRESS 



the usual modified ependymal cells with free extremities 

 projecting into its cavity. 



Our knowledge of the development of the pineal organ in 

 Amphibia is not in a very satisfactory condition, but Cameron 

 in 1903 brought forward a certain amount of evidence to show 

 that in frogs, toads and newts it has a paired origin. This 

 author maintains that in the cases investigated by him the 

 epiphysis or pineal gland arises in the form of two outgrowths 

 from the roof of the thalamencephalon, one on either side of 

 the middle line. The outgrowth on the right side disappears 

 very early, while that on the left gives rise to the adult epiphysis. 

 This is hardly what we should have expected, being exactly 

 the opposite to what takes place in bony fishes. It is of course 

 possible that the Amphibia, like the tuatara, differ from fishes 

 in this respect, but confirmation of Cameron's results is much 

 to be desired. 



Turning now to the Reptilia, we find, as already stated, 

 that amongst existing forms there are only two groups — the 

 Lacertilia and Rhynchocephala — in which a " pineal eye " is 

 still recognisable, although, just as in the case of the Amphibia, 

 we find clear evidence in the parietal foramen of many extinct 

 forms (e.g. Ichthyosaurus) that this organ was formerly more 

 widely distributed in the group, and probably of much greater 

 importance than it is at the present day. 



It was, as we have already seen, in certain members of the 

 group Lacertilia, viz. Anguis and Lacerta, that Leydig in 1872 

 first discovered the existence of a pineal sense organ. It was 

 in Anguis also that De Graaf in 1886 first clearly demonstrated 

 the eye-like structure of the organ in question, showing that 

 it consists of a hollow vesicle whose wall is differentiated into 

 a " retina" and a " lens," and which he regarded as the terminal 

 portion of the " epiphysis " constricted off from the remainder. 



The well-known researches of Baldwin Spencer in 1886 

 greatly extended our knowledge of the " pineal eye " in this 

 group and supplied us with details as to its structure in many 

 genera and species. This author showed that the organ varies 

 greatly in different forms, apparently according to the degree 

 of degeneration which it has undergone. Thus, while in such 

 forms as Anguis, Lacerta, and Varanus the eye-like structure 

 is still strongly in evidence, in Chamcelco it is reduced to a 

 simple vesicle, ciliated internally, and with no trace of 



