878 DEVELOPMENT AND STRUCTURE OF PINEAL EYE IN LACERTILIA, 



columnar cells of the thalamencephalon (fig. 2). The walls of both 

 vesicles are composed of a single layer of columnar cells with 

 oval nuclei. The nuclei, however, at this stage begin to undergo 

 karyokinesis, and a second row of columnar cells is formed. As 

 both vesicles increase in size they are carried more towards the 

 surface, and the appearance then presented is that of a hollow 

 stalk ending in the two evaginations, the whole being surrounded 

 by embryonic connective tissue. Since the cavity of the brain is 

 continuous with the cavity of the stalk and vesicles, we find that 

 the coagulable fluid which bathes the cerebral walls, is also present 

 in the latter (fig. 3, Hum.). 



Third Stage. — In this stage the anterior of the two vesicles 

 becomes constricted off" to form the pineal eye (fig. 4, Pa.) ; while 

 the posterior remains as the end of the epiphysis (fig. 4, Ep.). 

 When viewed at this stage the eye is seen to be a double-convex 

 body with a central cavity. Its superior and external portion is 

 the rudimentary lens composed of columnar cells, while the 

 inferior portion which is continuous vvith the lens, is the retinal 

 region likewise composed of columnar cells. The cavity between 

 is the optic vesicle containing the coagulable fluid referred to 

 above. No difi"erentiation has occurred in the retinal area up to 

 this stage, and I am unable to say what the structure in the adult 

 may be, as I have prepared no specimens. T may, however, 

 remark that the retina becomes densely pigmented, and so the eye 

 becomes very conspicuous when viewed as a solid object in the 

 adult form (fig. 17). And also, as far as I can ascertain, thei'e is 

 no connection between the eye and the epiphysis. 



The development of the eye of Gramiivdopliora is somewhat 

 similar to that of Lacerta as described by Hoff"mann.* 



HiNULIA. 



The stages I have of Hinulia have been from tiie time when the 

 eye is ditferentiated ofl" from the epiphysis. 



Position of Eye. — The eye lies close to the surface, being 

 separated from it only by a thin layer of connective tissue (fig. 5). 

 No scales are as yet visible on the surface of the embryo ; 



* Weitere Untersuch. zur Eatwicklungsgesch. der Reptilien. Morph. 

 Jahrb., XI., 176. 



