214 W. BALDWIN SPENCER. 



primitive structure of columnar cells, ciliated in- 

 ternally. In Cyclodus again we find another modification 

 present, the epiphysis having apparently reached a stage passed 

 through in the development of the eye of other Lacertilia; 

 a vesicle is formed distally, but the pineal stalk remains widely 

 open, very little pigment is present amongst the cells, and no 

 true eye is found. In Ceratophora, lastly, the distal 

 extremity of the epiphysis is placed within the cranial cavity 

 beneath the spot, corresponding in position to the parietal 

 foramen of other forms ; the portion equivalent to the optic 

 vesicle is present, forming a slightly swollen mass at the distal 

 extremity of the pineal stalk (?), consisting of rounded elements 

 very similar to those present in the extracranial part of the 

 epiphysis of Bufo cinerea. 



(3) External Modification. — When we come to deal with 

 the external modification it is very remarkable to notice that a 

 high development in this is by no means necessarily accom- 

 panied by, or the index of, a highly-developed sense-organ 

 beneath. InVaranus giganteus the external indication is 

 extremely well marked, whilst the eye beneath is also well 

 developed, and connected with the pineal stalk; in Hatteria, 

 on the other hand, the eye is still better developed, the retinal 

 elements being more clearly difi'erentiated, whilst there is quite 

 absent that great development of pigment which must indicate 

 to a certain extent degeneracy in the eye of Varan us. Despite 

 this there is in Hatteria no external modification, or, at all 

 events, only a very slight one present indicating the position of 

 the eye beneath ; the latter also lies deeply embedded in connec- 

 tive tissue — deeper still than in the case of Varan us — though, as 

 in every other form, there is a marked absence of pigment 

 between the eye and the surface of the head. Thus, in the one 

 of these two forms in which the organ is most highly de- 

 veloped, we find that the external modification is much the 

 least evident. If, again, such genera as Calotes, Seps, 

 Leiodera, and Anolis be taken, in these the modified scale 

 is so prominent as to form the most noticeable feature on the 

 dorsal surface of the head, and to resemble a cornea; below it 



