20 S. B. VINCENT 



other animals and forms a rich plexus of medullated, unmedul- 

 lated, pale and varicose fibers. The touch cells are similar to 

 those of other animals and in a similar position. He thinks the 

 beard hairs of men lie structurally between the usual body hairs 

 without the root sheath swelling and the tactile hairs of other 

 animals. 



We will neglect entirely the discussion as to whether hairs 

 originally developed from the scales of reptiles or fishes or from 

 the Becher organs of amphibia, but there is one \dew of the 

 course of their development that is not without interest for us. 

 Many believe the theory which Botezat advances that the com- 

 mon body hairs are retrogressive, that the tactile hairs were 

 primary in development but that as functional need changed the 

 greater part lost their root sheaths and high degree of innervation 

 and came to serve more and more as a mere body covering. 



As to the higher development of these tactual organs in some 

 animals than in others, Edinger ('08) calls attention to the large 

 fiber tract leading from the nucleus of the trigeminus to the 

 tuberculum olfactorium in birds and some other animals. He 

 thinks the increase in size of this lobe in some instances due to 

 the "importance of the beak which is innervated by the trigemi- 

 nus" and ''the extraordinary rich trigeminal supply about the 

 mouth and in the tongue." Probably other fibers find a center 

 in or about the anterior perforated space but Edinger' s emphasis 

 of the 'oral sense' has not been without value. We must recog- 

 nize that the mouth parts of animals have a much more varied 

 functional significance and are of far greater relative importance 

 in them than in man. 



VI. FUNCTION 



The generally recognized character of the tactile hair is implied 

 in its name. The purpose of such sense organs about the mouth 

 has never been satisfactorily explained. They are not confined to 

 nocturnal animals, as Odenius thought ('66), nor do they have 

 chiefly to do with the size of openings. 



In a long series of experiments with animals in open, elevated 

 mazes and in problem boxes, some facts were established as to 



