Animal Behaviour 



to jump through it, and they may struggle at the impossible 

 task of working their way into the soHd white surface made by 

 the leaf edges of a closed book. 



That frogs are attracted by light and have definite orienta- 

 tion in regard to it sometimes produces interesting results when 

 frogs are in captivity, where the light comes strongly from one 

 or two directions only. The same response to the same stim- 

 ulus may place six or eight pickerel frogs in a row, each in resting 

 position with toes tucked under and head resting meekly on the 

 body of the frog in front of him; or a half-dozen green frogs 

 may make burrows in the moss side by side in a row and sit in 

 the burrows all facing the same way — six pairs of bright eyes 

 alert and contented. 



In increased temperatures the positive response to light is 

 still greater up to a temperature of 30° C. Above this, the frogs 

 move away from the light instead of toward it. In decreased 

 temperatures, the response is less until at 10° C. frogs move away 

 from the light (negatively phototactic). This is true whether the 

 frogs are in air or water. Experiments ^ which have proved this 

 are interesting because of the explanation they give of the aesti- 

 vation habits of the Salientia in the high summer temperatures 

 of Texas and Mexico and the hibernation habits during the win- 

 ters at the north. Green frogs kept in a moss vivarium in win- 

 ter remain out on the moss in normal temperatures, but disap- 

 pear under the moss at once if the temperature of the room drops 

 much below normal, or if a window is opened and the cold wind 

 is allowed to blow over them. 



Many North American frogs and toads show protective in- 

 stincts or racial habits, the immediate cause of which seems to 

 be unusually strong stimuli acting on the nervous system. When 

 a toad, frog, or tree frog is disturbed suddenly, it may fill the 

 lungs with air until they puflF out at the sides, making the crea- 

 ture as broad as long. At the same time, the head is lowered 

 to the ground and the frog certainly looks on the defensive. It 

 seems reasonable that it would prove well-nigh invulnerable to 

 the attacks of an enemy like the snake that expected to swallow 

 it whole and head first. 



A toad very often flattens and spreads the body and remains 

 motionless on the ground when startled by the approach of an 



* The Response of the Frog to Light. E Torelle, American Journal of Physiology, vol. 9. 



33 



