REACTIONS OF PROBOSCIS OF PLANARIA 91 



fixed to the slide that when water was added it appeared as a 

 distorted mass which the freed proboscis was ingesting. More- 

 over, the proboscis when inactive lies within a sheath, the walls 

 of which lie more or less in contact with the quiet proboscis. 

 It has been noted that, when the proboscis is extended to pro- 

 ject from the mouth of the sheath, the part that lies free is the 

 portion of the proboscis that is actively contracting and mov- 

 ing. The part within the sheath shows little or no activity until 

 food passes through it. Hence we tentatively inferred that ab- 

 sence of contact with the w^alls of the proboscis-sheath excites 

 the proboscis into activity. 



The following experiments were made to determine whether 

 the absence of thigmotactic stimuli excites the proboscis beyond 

 the inhibitoiy control of the central nervous system. 



1. A specmien had its anterior and posterior ends cut away 

 (fig. 3, B). Next an additional part of the anterior end was am- 

 putated. There was up to this step no reaction on the part of 

 the proboscis (fig. 3, C). The posterior half of the proboscis- 

 sheath was next cut away arid as yet the proboscis remained quiet 

 (fig. 3, D). When, however, all of the sheath was removed, al- 

 though the proboscis remained joined to the fragment of body 

 at its base and hence in connection with a part of the central 

 nervous system, it became active at once, turning upon the frag- 

 ment of bod}^ and ingesting part of it (fig. 3, F). Finallj^, the 

 proboscis underwent autoamputation and swam about attempt- 

 ing to ingest objects. This reaction and autoamputation of the 

 proboscis may have been due, in this case, to a mechanical 

 injury of the central nervous system. 



2. In this second experunent we had the proboscis incited to 

 activity under other conditions. Here, after the anterio and 

 posterior ends had been removed (fig. 5, B), the proboscis left 

 the sheath when an effort was made to pull away the sides of the 

 proboscis-sheath with two needle points. While the sheath was 

 thus temporarily spread the proboscis swam out. Here again 

 there was a temporarj^ disturbance of the thigmotactic condi- 

 tions existing between the proboscis and its sheath; but the ques- 

 tion of disturbing the central nervous system, during the opera- 

 tions, also presents itself. 



