78 The Animal Mind 



resting planarian shows a decidedly lowered susceptibility to 

 stimulation. Bardeen found that if the animal was not 

 already in motion, it gave no positive response to food in 

 its neighborhood (10). 



20. The Chemical Sense in Annelids 



In our own experience, as has been said, the "food sense" 

 is represented by the two senses taste and smell, the stimulus 

 for the one being fluid, and that for the other gaseous, so that 

 the latter enables us to perceive objects at a distance. For 

 water-dwelling animals, such as most of those whose behavior 

 , we have been describing, the distinction evidently cannot 

 ' well be drawn. If such an animal perceives food at a dis- 

 tance, the stimulus is necessarily diffused through the water, 

 and Lloyd Morgan has proposed the term " telaesthetic taste" 

 for the sense which makes such perception possible (279, 

 p. 256). The term indicates that this sense corresponds to 

 taste in an air-dwelling animal because the stimulus is fluid, 

 but differs in that it allows perception of a distant object, as 

 taste in the ordinary sense does not. In the most familiar 

 representative of the Annelida or segmented worms, the com- 

 mon earthworm, as in the land planarian, a distinction analo- 

 gous to that between smell and taste in our own sensory 

 experience may be made ; in the leeches and marine annelids 

 it cannot. 



Gentle and continuous mechanical stimulation produces in 

 the earthworm "positive thigmotaxis " ; that is, the animals 

 have a tendency to crawl and lie along the surface of solids 

 (387). That there is some discrimination of edible from 

 inedible substances when in contact with the body Darwin 

 thought probable from the apparent preference of the worm 

 for certain kinds of food (91). In the earthworm Allolobo- 

 phora fatida we find a differentiated response to contact 



