132 CALVIN P. STONE 



and refinement of technique the activation of the copulatory 

 response can be described as completely as many of the well 

 known reflexes have been described by the physiologists (Sher- 

 rington '06). 



1. Experimental control of exteroceptors 



From what is known of the functioning of receptors in the 

 activation of well known reflexes (Sherrington '06) it may be 

 inferred, for the purpose of setting up definite working hypothe- 

 ses that their functions in the initiation of the copulatory act in 

 the rat may be about as follows : 



1. They may serve to locate other animals of the same species 

 or animals capable of arousing sexual excitement in the male. 

 As distance receptors they may set up seeking activities. 



2. They may serve to differentiate the sexes. 



3. They may have a selective sensitivity for certain kinds of 

 stimuli arising from the female in heat. And by means of direct 

 efferent connections with the ganglionic centers concerned with 

 the reproductive mechanism may transmit the necessary impulses 

 to arouse this mechanism to action. 



4. They may serve to reinforce nervous processes underlying 

 the sexual response, even though they have no direct reflex con- 

 nections with the essential reproductive mechanism. 



5. Or, by exciting glandular activities, they may cause secre- 

 tions to be released into the blood stream which have the special 

 function of sensitizing or giving tonus to the neuro-muscular 

 mechanism involved in the act of copulation. 



Each of the foregoing possible functions must be tested in 

 the light of available experimental data to determine w r hich if 

 any of them are really involved in the initiation of the sexual 

 act. 



A. Vision. Very few references to the visual receptors in the 

 literature on sex-studies indicate clearly the role of visual stimuli 

 either as facilitators or excitors of sexual responses. Examples 

 of the courtship of birds and other animals through display of 

 special adornments or by movements of a particular kind are 

 cited by Morgan ('00, p. 61 ff.) and others. In this case the 



