54 Trans. Acad. Sci. of St. Louis 



this instinct is now detrimental to the opossum, Inger- 

 sol thinks it a survival of a time when it was of value. 

 He reminds us that the opossums rank among the most 

 primitive mammals, and that when they appeared none 

 of the higher mammals had been evolved. The reptiles 

 were then the monarch of land, air and water. Many 

 of them were gigantic beings but, judging from the 

 size of their skulls, they must have been of a very low 

 order of intelligence, probably lower than our present 

 alligators. The indications are that these ancient rep- 

 tiles fed exclusively upon live prey. Small objects would 

 not have attracted the attention of such stupid creatures 

 unless they moved. It is easy to see how this death- 

 feigning behavior would be of value to an opossum under 

 those conditions. IngersoU thinks that the instinct ap- 

 peared and was perpetuated at that time. Wlien one 

 recalls the gigantic size of many of those reptiles and the 

 small size of the opossum, although IngersoU does not 

 say so, the death-feigning of these marsupials might have 

 arisen as a case of terror paralysis. 



If IngersoU 's interpretation of the origin of the leti- 

 simulation of the opossum is correct, we seem justified in 

 saying that in both the opossum and in insects death- 

 feigning is but an exaggerated prolongation of the pause 

 made by most animals when startled. Although, until 

 other experiments are forthcoming, we must suspend 

 judgment about the nature of the letisimulation of many 

 of the higher mammals, so far as the insects and the 

 opossum are concerned, we can exclaim with James : " It 

 really is no feigning of death at all and requires no self- 

 command. It is simply terror paralysis which has been 

 so useful as to become hereditary." 



