2i6 Studies in Animal Behavior 



species has its basis in the thigmotaxis of the aquatic 

 forms. As the species studied become more terres- 

 trial in habit, the thigmotaxis becomes gradually 

 specialized into a typical instinct of feigning death. 



Many facts indicate that death feigning in insects 

 and other forms has had a similar origin in the 

 thigmotactic response. It is a rather striking fact 

 that, with very rare exceptions, it requires some 

 form of contact stimulus, it may be but a touch, jar, 

 or even a breath of air, to elicit this instinct. One 

 of the very few exceptions to this rule which has 

 been recorded is afforded by Carausius, whose death 

 feint, according to Schmidt, arises from internal 

 causes, and cannot be induced by any discoverable 

 environmental agency. Should it be definitely estab- 

 lished that this case is truly one of "autocatalepsy," 

 as it has been called by Schmidt, it would not be 

 fatal to the supposition that it began originally as a 

 reaction to contact; for it is not without precedent 

 that an instinct having originated with reference to 

 one feature of the environment should finally come 

 to be set into operation by a quite different cause. 



Those cases of death feigning in which there is a 

 limp and relaxed condition of the musculature, such 

 as occurs in some birds and mammals, may have an 

 origin quite different from that of the more preva- 

 lent cataleptic type. The suggestion that death- 

 feigning had its origin in the partial paralysis pro- 

 duced by fear may perhaps apply to cases such as 

 these, although this explanation cannot, I feel sure, 



