508 ADAPTATIONS TO PHOTIC QUALITY 



results on the dog and cat, obtained only negative results also with the 

 raccoon. This species is thus in the same boat with the dog : if it has any 

 color sensations, they are so vague and unsaturated that some individuals 

 are not even conscious of them at all; and to other individuals, they can- 

 not be made to have meaning. 



Despite the alleged interest of the mink in red objects, the mustelids 

 which have been studied at all carefully have shown no evidence of hav- 

 ing color vision. Miiller, in 1930, dyed some hen's eggs red, green, blue, 

 gray, and white. His captive marten (Martes foina, a close relative of 

 our Martes americana) was allowed to come for them and take them, 

 one by one, to its cache in a corner of the cage. The animal took the eggs 

 in various sequences in successive tests, evincing no indication that any 

 one egg seemed brighter than another or that any color was especially 

 attractive or repellant. MuUer's extensive studies of the psycho-physiology 

 of this species led him to rank olfaction above hearing in importance for 

 the animal, with vision a poor third on the sensory list. 



Miiller did more work with the polecat, Putorius putorius, a type of 

 mustelid for which there is no exact American counterpart, but which is 

 the wild ancestor of the domestic ferret seen here occasionally in the 

 capacity of professional rat-catcher. Miiller rated the sensory modalities 

 of the polecat all lower than those of the stone-marten, but in the same 

 order of value. The polecat could be trained to discriminate brightnesses, 

 but not colors. It was taught to distinguish between red and blue papers, 

 but when these were placed among other colored and gray papers the 

 animal was lost. The species is either totally color-blind or perhaps, like 

 the dog and raccoon, excessively color-weak. All in all, the evidence for 

 color vision in carnivores is practically nil. 



Turning to the rodents, we find ourselves in a most controversial sub- 

 ject. On some of the selfsame species, equally strong claims both for and 

 against color vision have been advanced. While the squirrels are set off 

 sharply from other rodents by their diurnal habits and cone-rich or pure- 

 cone retinae, strangely enough the evidence for color vision in them is no 

 better and no worse than that relating to some of the most strongly noc- 

 turnal rodents, whose possession of any cones at all is questioned by 

 some retinologists. 



In all, three kinds of squirrels, six other rodents, and one lagomorph 

 have had experimental attention. Most of the studies have been made 

 upon the common laboratory species. Watson and Watson, in 1913, 

 studied the rat with a spectral light technique. They trained rats positive 



