REACTIONS OF PROBOSCIS OF PLANARIA 89 



FACTORS DETERMINING INHIBITION OF THE PROBOSCIS 



We have been interested most in an effort to determine what 

 the inhibitory influenced are which control the fixed proboscis 

 in such manner that it rarely ingests objects under conditions 



Fig. 3 B, dorsal ganglia and posterior extremity of body cut away; C, more 

 of anterior portion of body removed; D, posterior half of proboscis-sheath cut 

 away; E, entire proboscis-sheath removed, proboscis becoming active {F); G, 

 proboscis active after autoamputation; H, proboscis inactive after oral fourth 

 was cut away. 



favorable to microscopic study, thus making the fixed proboscis 

 stand in sharp contrast to the freed proboscis, which latter 

 under laboratory conditions may readily be demonstrated in- 

 gesting food and other solid objects. It has occurred to us 

 that one of these inhibitory factors may be external and the 

 other internal. 



