182 



LILLIE AA-D KNOIVLTON. 



[VOL. I. 



dency to form a bifid tail at 3 C. ; but the process was slow 

 and never went very far. 



At temperatures above the maximum no abnormalities were 

 found ; at 32 the planarians regenerate partly; small eye-spots 



180 

 170 

 1 60 



140 

 130 

 1 20 



I 10 

 IOO 



90 



80 

 70 

 60 



50 

 40 



30 



20 

 IO 



10 



15 



20 



35 



FIG. i. Curve of regeneration of the posterior half of Planaria torva at different temperatures. 

 The ordinates measure time in days and the abscissae temperature in degrees Centigrade. 



may appear, and death occurs in about six days ; at 33 there 

 was very slight regeneration, the animals dying within three 

 clays. At 34 and above there was no regeneration, and death 

 came on rapidly. 



2. The Early Development of Ainblystoma tigrinuin and the 



Frog (Rana virescens}. 



The eggs of Amblystoma are laid in March, often before the 

 ice is entirely out of the ponds, when the temperature of the 



