VISION IN THE MOUSE 595 



will be overcome by the impulse to avoid the unpleasantness of 

 the shock which ensues in case of failure, so that the animal be- 

 comes unwilling to venture at all. 



In the case of the human being, if several repetitions are neces- 

 sary to bring into the focus of consciousness the movements that 

 that being is making, then we must not expect much of the mouse, 

 and we must believe that a large number of the cases recorded as 

 failures were not necessarily failures to discriminate between 

 stimuli but, rather, secondarily automatic movements. 



When a visual stimulus succeeds in calling forth a change in 

 mode of action as its response — thus overcoming the kinaesthetic 

 influences, which would tend to bring about a former mode of 

 action — there is involved a discharge of energy through the higher 

 association tracts and a conscious accompaniment. The law of 

 parsimony proposed at the beginning of this section, and also our 

 general observations, forbid us to assume that such conscious 

 accompaniment is involved, but rather make for the view that 

 the mental processes of the animal rise into consciousness of its 

 movements at intervals not so frequent as in the human being, and 

 that the kinaesthetic sense is the predominant directive sense in 

 the mouse. 



IV. STRUCTURE OF THE EYE OF THE MOUSE 



The animals used for the anatomical study of the eye were 

 from among those that had been used in the experiments. Some 

 gray mice were chosen and some albinos ; also a few dancing mice 

 were included among those studied. 



Method: The heads of mice that had recently died or had 

 been killed were preserved in formol-alcohol. When ready to 

 work with them , the eyes were removed and put through alcohols 

 of increasing strength, for about an hour in each, up to 100 per 

 cent. They were then transferred to xylol where they cleared over 

 night and the next day they were put in soft paraffin for an hour. 

 They were next placed in hard paraffin for a half hour and later 

 imbedded in this same paraffin. Care was taken in the imbedding 



