VI.] 



139 



A. Diagrammatic section taken perpendicular to the plane of 

 the paper, along the line y, y, Kg. 49. The stalk is not 

 seen, the section falling quite out of its region, vh, hollow 

 of optic cup filled with vitreous humour ; other letters as in 

 Fig. 47 B. 



B. Section taken parallel to the plane of paper through Pig. 49, 

 so far behind the front siirface of the eye as to shave off a 

 small portion of the posterior surface of the lens I, but so 

 far in front as not to be carried at all through the stalk. 

 Letters as before ; /, the choroidal fissure. 



C. Section along the line z, 2, perpendicular to the plane of the 

 paper, to shew the choroidal fissure /, and the continuity of 

 the cavity of the optic stalk with that of the primary optic 

 vesicle. Had this section been taken a little to either side of 

 the line z, z, the wall of the optic cup would have extended 

 up to the lens below as well as above. Letters as above. 



sented (the superficial epiblasfc of the head would also 

 be shewn) ; but there would be nothing seen of either 

 the stalk or the fissure. If on the other hand the 

 section were taken in a plane parallel to the plane of 

 the paper, at some distance above the level of the 

 stalk, some such figure would be gained as that shewn 

 in Fig. 50 B. Here the fissure / is obvious, and the 

 communication of the cavity vh of the secondary vesicle 

 with the outside of the eye evident; the section of 

 course would not go through the superficial epiblast. 



