40 STELLA BURNHAM VINCENT 



group. Experiment VI gave the olfactory control and VII in- 

 creased the tactual, contact difficulties without adding anything 

 really new. When, however. Experiments VIII and IX were 

 finished, it was seen that sight and contact may serve together or 

 interchangeably for some problems, although the loss of either 

 raises difficulties, but that the loss of both, or rather the efficient 

 means of using both, makes difficulties almost too great to be 

 overcome. 



Previous histological and structural studies had shown that 

 the tactile hair is a powerful tactile organ and that this is due ; — 



(a) To its great innervation. 



(b) To the leverage which magnifies the stimulus. 



(c) To the vibratory nature of the stimulus which is the 

 on^y adequate stimulus for some reflexes, which summates sub- 

 liminal stimuli, which prolongs the initial stimulus. 



(d) To its muscular connections which transmit stimulus 

 over large areas. 



(e) To its haemostatic apparatus which permits free vibra- 

 tion of the hair to the depth of the folHcle, which perhaps in- 

 creases or modifies the pressure, which may raise or lower the 

 nervous threshhold and which may possibly have some chem- 

 ical significance. 



The studies here reported prove: — 



1. That these hairs have several important functions in the 

 acquisition of such coordinations. 



2. That these have not been observed in the ordinary maze 

 because its mode of construction safe-guarded the animal at the 

 very points where these sense organs are most efficient. 



3. Open running, especially where footing is difficult, reveals 

 different behavior. 



4. Extending as they do sometimes two inches beyond the 

 head, the hairs become in this sense "distance sense" organs 

 whose office is probably chiefly protective. 



5. Those curved hairs most anterior sweep the surface upon 

 which the animal runs and the constant sensations thus aroused 

 probably contribute largely to the "sense of support." 



6. The failure of these sensations is warning of a void and 

 throws into action powerful reflexes which save the animal 

 from danger of falls. 



