6o 



THE BIOLOGY OF THE FROG 



CHAP. 



right position. According to Verworn, 1 the muscles involved 

 in the righting movements are in a state of tonic contrac- 

 tion as if these movements were suddenly inhibited. The 

 breathing movements and the heart beats are at first accel- 

 erated, but at a later stage their rate falls below the normal 

 (Heubel), and there is a decreased responsiveness to ex- 

 ternal stimuli. Dif- 

 ferent frogs vary 

 greatly as regards 

 both the ease with 

 which they may be 

 hypnotized, and the 

 duration of the hyp- 

 notic state. In some 

 cases if a frog is sim- 

 ply placed on its back 

 without being held, 

 it may become hyp- 

 notized after it has 

 righted itself a few 

 times, and lie for a 

 long time in some 

 phase of the pro- 

 cess of turning over. 

 Specimens of Rana 

 esculenta, according 

 to Verworn, when laid on their backs, sometimes quickly 

 draw the hind legs close to the body, close their eyes, and 

 lie with their muscles in a state of tonic contraction, — a 

 condition which suggests the death feigning of certain 

 insects. 



Tonic contractions of different parts of the body may 



1 Verworn, " Die sogenannte Hypnose der Thiere," 1898. 



FIG. 7. — Rana temporaria in the so-called 

 hypnotic state. The upper figure shows 

 the position assumed when the back is 

 rubbed with the finger. The same attitude 

 is maintained when the frog is placed on 

 its back, as is shown in the lower figure. 

 (Modified from Verworn.) 



