Proc. Roy. Soc. Edin.] 
[Vol XXXIII. 
Fig. 5. — Acid-etched ground glass, x 100. Fig. 6. — Images of a luminous point formed 
by the pits acting as lenses, x 100. 
Fig. 7. — Images of a luminous cross formed by the pits 
acting as lenses. xlOO. 
Dr James Robert Milne. 
I Plate II. 
