138 



THE THIRD DAY. 



[chap. 



much the appearance represented in the diagram 

 Fig. 49. 



A section of such an eye taken along the line y^ 

 perpendicular to the plane of the paper, would give a 

 figure corresponding to that of Fig. 50 A. The lens, 

 the cavity and double waUs of the secondary vesicle, and 

 the remains of the primary cavity, would all be repre- 



DlAGRAMMATIC REPRESENTATION OF THE EtE OF THE OhICK 

 OF ABOUT THE ThIRD DaY AS SEEN WHEN THE HEAD IS 

 VIEWED FROM HNDERNEATH AS A TRANSPARENT OBJECT. 



I the lens, V the cavity of the lens, lying in the hollow of the 



optic cup. 

 r the anterior, u the posterior wall of the optic cup, c the cavity 



of the primary optic vesicle, now nearly obliterated. By 



inadvertence u has been drawn thicker than r, it should 



have been thinner throughout, 

 s the stalk of the optic cup with s its cavity, at a lower level 



than the cup itself and therefore out of focus ; the dotted 



line indicates the continuity of the cavity of the stalk with 



that of the primary vesicle. 

 The line z, e, through which the section shewn in Fig. 50 is 



supposed to be taken, passes through the choroidal fissure 



