198 The Animal Mind 



come down to the bottom of the cage for food when a card 

 bearing the word "Yes" printed on it was exposed, and to 

 stay up when one bearing the letter "N" was shown. The 

 conditions seem to have been complicated, however, by the 

 fact that the two cards were not placed in quite the same 

 position. Further tests with cards carrying various designs 

 showed varying degrees of capacity to distinguish them on 

 the part of the monkeys (397). Kinnaman got negative 

 results with his two Macacus monkeys in attempting to 

 train them to distinguish cards such as those used in the later 

 experiments of Porter on birds. His monkeys, however, 

 proved able to distinguish vessels of different forms, "a wide- 

 mouthed bottle, a small cylindrical glass, an elliptical tin 

 box, a triangular paper box, a rectangular paper box, and a 

 tall cylindrical can.' 7 These vessels differed in size as well 

 as in form (221). 



Special evidence of the comparative development of the 

 visual image in different genera of ants is suggested by 

 Wasmann to be furnished by the facts of mimicry. Certain 

 insects belonging to orders other than the Hymenoptera 

 inhabit ants' nests, and have in many cases become more or 

 less modified to resemble their hosts. Wasmann thinks 

 that these resemblances, which have been established on 

 account of their protective value, are in insects living among 

 ants of well-developed visual powers, such as would deceive 

 especially the sense of sight, while in the "guests" of ants 

 whose vision is poor, the mimicry is adapted to produce 

 tactile illusions (426). 



78. Class V : Reactions adapted to the Distance of Objects 

 The factors that make possible the perception of the third 

 dimension, depth, or distance outward from the body, in in- 

 vertebrate animals are little known. Certain invertebrates do 



