1 8 Journal of Comparative Neurology and Psychology. 



The behavior of young pigeons, chicks, kittens and pup- 

 pies in unusual spatial conditions has been studied most fully by 

 Mills ('98, p. 150), who in discussing the "sense of support" 

 writes: "I have found in the case of all puppies, and several 

 other kinds of animals examined, that even on the first day of 

 birth they will not creep off a surface on which they rest, if 

 elevated some little distance above the ground. When they 

 approach the edge they manifest hesitation, grasp with their 

 claws or otherwise attempt to prevent themselves falling, and, 

 it may be, cry out, giving evidence of some profound disturb- 

 ance in their nervous system. 



"It would seem that there is no more urgent psychic neces- 

 sity to young mammals than this sense of being supported. 

 All their ancestral experiences have been associated with terra 

 firma, so that it is not very surprising that when terra firina seems 

 about to be removed they are so much disturbed. To my own 

 mind this is one of the most instructive and striking psychic mani- 

 festations of young animals, though I am not aware that any 

 attention has been called to it before ; and instead of referring 

 to it under any of the usual divisions of sense, as the muscular 

 sense, pressure sense, etc., I prefer to treat the subject under 

 the above general heading (Sense of Support), for it seems to 

 me that the feeling is a somewhat complex one. 



"It is interesting to note that a water tortoise I have had 

 for a number of )-ears will at any time walk off a surface on 

 which he is placed. But this is not a creature that always is on 

 terra firina in the same sense as a dog, but it frequently has 

 occasion to drop off logs, etc., into the water. But again, I 

 find this sense of support well marked in birds which drop 

 themselves into 'thin air'. Nevertheless, a consideration of an- 

 cestral experiences throws light on most cases, and perhaps on 

 this one also." 



Concerning white rats. Small ('99, p. 93) states that "as 

 early as the second day (after birth) they show an uneasiness 

 when on the edge of a void — sometimes drawing back, some- 

 times manifesting their dominant trait of curiosity by leaning 

 over and sniffing. At the age of four or five days the presence 



