PINEAL EYE IN LACERTILIA. 229 



method of development; at any rate, without laying undue 

 stress upon the example to be quoted, it is worth while drawing 

 attention to it, inasmuch as it reveals to us the possible path 

 by which the epiphysis of higher forms has been developed out 

 of a structure similar to the larval Tunicate eye at an early 

 stage. De Graaf, in his recent memoir,^ figures and describes 

 the development of the epiphysis in Bufo ciuerea. His 

 figures are, unfortunately, not drawn with such regard to his- 

 tological detail as could be desired in the present instance, but, 

 so far as they go, they indicate the possible existence of a con- 

 nection between the epiphysis of B u f o and the azygos eye of 

 the embryo Tunicate. He shows the epiphysis as arising at 

 first as a thickening of the roof of the thalamence- 

 phalon, which soon assumes the form of a slight 

 hollow outgrowth. On the inner surface of the cells, 

 sharing in the thickening and subsequent outgrowth, 

 is a small but well-defined mass of pigment. This pig- 

 ment very soon entirely disappears, and a hollow process — the 

 epiphysis — is formed, which gradually increases in size, and 

 becomes differentiated into a vesicular distal portion and a 

 solid stalk, the former gradually becoming constricted off. Is 

 it not possible that in these phenomena we have an indication 

 of the change from the internally situated Tunicate eye into an 

 externally placed hollow process ? As before said, the Tunicate 

 eye arises as a distinct thickening of the brain-roof, the cells 

 forming the thickened portion bearing pigment on their in- 

 ternal ends. Just the same phenomena are witnessed in the 

 case of the epiphysis of Bufo cinerea, but, instead of develop- 

 ing into an eye internally placed, the cells, whose external 

 ends already form a bulging on the outer surface, form into 

 a well-defined evagination, the internally placed pigment dis- 

 appears, and the epiphysis, as present in all the higher groups 

 of the Chordata, is developed. 



Whether we are here presented with an epitome of the steps 

 passed through during transformation of the internally-placed 

 eye of a transparent organism into the externally -lying evagina- 

 1 Op. cit., pi. iii, figs. 22 and 23, p. 27. 



