

7^' '.J/-r^? 





••<!>-•:':>■ 





Frontispiece 



Epithelial cells from the dorsum of an Axolotl tadpole, showing range of contrast control for 

 unstained tissue with Spencer phase microscope. 500 X. A, brightfield; B, darkfield. C-D, 

 low and medium B— dark-contrast phase. E-G, low, medium, and high A— dark-contrast 

 phase. H-J, low, medium, and high A-|- bright-contrast phase. Note details at arrows. 



