30 



First or normal type. 



Second or transitional 

 type. 



Third or reversed type. 



THE SIGNS OF LIFE 



Dark. Light. 



LLECT. 



OOO3t 



O 



D&rk. 



I mm. 



am ins 



FIG. 13. Frog's eyeball. The three types of its response to light, 

 as described in the text. 



