. The biology of the amphibia. Amphibians. 424 THE BIOLOGY OF THE AMPHIBIA Many frogs and toads when pinched will open their mouths and give a shrill cry. It would seem to be an important frighten- ing device, although critical field observations concerning its effectiveness are lacking. Hinsche (1923) finds that this fright- ening reaction may be induced in Bufo, but the toad opens its mouth and straightens its legs without producing a sound. Hinsche (1928) has shown that the head-bending and leg- straightening reaction is part of a complex series of defense reac- tions common to many Salient
. The biology of the amphibia. Amphibians. 424 THE BIOLOGY OF THE AMPHIBIA Many frogs and toads when pinched will open their mouths and give a shrill cry. It would seem to be an important frighten- ing device, although critical field observations concerning its effectiveness are lacking. Hinsche (1923) finds that this fright- ening reaction may be induced in Bufo, but the toad opens its mouth and straightens its legs without producing a sound. Hinsche (1928) has shown that the head-bending and leg- straightening reaction is part of a complex series of defense reac- tions common to many Salientia. In the course of phylogeny, some parts of this series of reflexes, such as the warning cry, are lost, while other phases, such as the pushing with bowed head, are modified. It is interesting that the more terrestrial Salientia should exhibit the series of reflexes in their most developed form. As discussed in another chapter (page 381), many reflexes, such as the "unken reflex" and the scream reaction, exhibit a gradual. Fig. 137.—Ensatina eschscholtzii defending itself against a Ring-necked Snake. {After Hubbard.) modification in phylogeny but the change is not always closely correlated with an obvious utility. Tonic Immobility.—Salamanders, frogs, and toads may be readily thrown into a state of tonic immobility which, under certain circumstances, may prove a protective measure. Young toads when picked up will frequently partially contract their limbs and become immobile (Mangold, 1925). This behavior has been compared with the hypnotic state produced in man by suggestion. It is commonly seen in such salamanders as Plethodon and Ambystoma, which when handled gently often exhibit a "death ; It may be most readily induced in both frogs and salamanders by placing the individual on its back and holding it there a moment. The death feint usually lasts only a few minutes, but it may be prolonged over an hour if disturbing sensory impressions are avo
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