MOVEMENTS, ETC., OF FRESH-WATET^ PT-ANAIHANS. C37 



tlio reason for the statement of Bnrdeen (loc. cit., p 522) '' that 

 worms which liaJ been kept in pure rain water for a week or 

 two, and were thus in a hungry condition, would remain 

 unmoved by the presence close by their side of a piece of 

 fresh snail, a food much prized by them," 



1 . Food Reactions of Specimens after Opera- 

 tions. — For the purpose of throwing" light on the general 

 mechanism of the food reaction, experiments were tried on 

 specimens cut in different ways. It is unfortunately very 

 different from practical reasons to get many certain results 

 from these experiments. Many of the results are negative, 

 and hence not entirely conclusive. Since, however, some 

 important facts have been brought out by these experiments, 

 they will be described. 



The first operation which will be discussed is that of 

 cutting the animal in two transversely. If such a cut is 

 made in the region in front of the pharynx, the anterior 

 resulting piece, after it has recovered somewhat from the 

 shock effect of the operation, will show the following reac- 

 tion. On coming into the zone of diffusion about a piece of 

 meat it gives the positive reaction just as a normal worm 

 does, and turns towards the food. On reaching the edge of 

 the meat its behaviour is again like that of the normal 

 animal ; it stops, usually " grips " the food, and then passes 

 on over it. At this point appears the striking difference 

 between the behaviour of this anterior piece, which, it must 

 be remembered, has no pharynx, and the behaviour of the 

 entire worm. The anterior piece after gripping the food 

 glides up over it, and without the slightest change, even in 

 the rate of gliding, passes down off of it on the other side. 

 There is not the slightest indication of any stopping for the 

 pharynx to be extruded. 



If the transverse cut is made farther back, so that the 

 pharynx is included in the anterior piece, this will then 

 behave with reference to food quite as a normal animal does. 

 It will stop on the food and extrude the pharynx. 



The posterior pieces resulting from transverse cuts do not 



VOL. 40, PART 4. NEW 3EKIES. TT 



