144 



ELEMENTARY BIOLOGY. 



[CHAl 



p. Their free ends ; fimbriated and prolongec 

 down among the rods and cones. 



/. The fibres of Miiller ; highly refractive sup-j 

 porting fibres, often traceable with ease froi 

 the internal limiting membrane to the fenes 

 trated layer. 



iii. Obtain, if possible, similar sections which shall 

 pass through the entrance of the optic nervej 

 Examine under a high power, and follow th( 

 course and relations of the nerve-fibres. 



iv. Take a fresh frog's eye : prick its cornea and col- 

 lect the aqueous humour on a slide. Then opei 

 the eye, remove a bit of the retina and tease it 

 out in the aqueous humour, mount and examine 

 with a high power. 

 a. Numerous rods will be seen floating about,] 

 many broken but some intact and showing th( 

 boundary line between their two segments very| 

 plainly. At first both segments are homoge- 

 neous, but very soon they begin to alter; th( 

 outer layer frequently then gets transversely 

 striated and shows a tendency to split up int( 

 several pieces : gradually these rods curl upj 

 swell out, and entirely disintegrate. 



13. The olfactory epithelium. 



Open the nasal sac of a frog ; remove a portion oi 

 the epithelial lining and transfer to i p. c. osmi( 

 acid solution for 2 — 3 hours; tease up in weak] 

 glycerine and examine with your highest power. 



Numerous mutilated cells will be found, and,l 

 among them, more or less perfect representatives] 

 of the following. 



