28 STEREOTROPISM OF THE DOGFISH 



structures could exist which would have the effect of synapses. It 

 must be admitted, however, that notwithstanding the closeness of 

 the analogy, the reversal of the heliotropic and of the stereotropic 

 reactions may be due to totally different mechanisms. 



SUMMARY. 



1. The dogfish responds to certain contact stimuli by definite 

 stereotropic reactions. These reactions can be positive or negative. 



2. The sense of the stereotropic response depends on the strength 

 of the stimulus; a "weak" stimulus, produces a positive and a "strong" 

 stimulus, a negative response. 



3. The strength of stimulus necessary to cause a reversal of the 

 reaction depends in part on the physiological state of the animal. 



4. The stereotropic reactions occur equally well in the absence of 

 the forebrain. 



