G38 T^AYMOND TRAliL. 



give any definite food reaction, so far as I have been able to 

 ascertain, until they have been regenerated to some con- 

 siderable extent. Posterior pieces from which only the head 

 has been cut will glide by pieces of snail on which other 

 worms are feeding, without giving the slightest reaction.^ 

 In experiments so arranged that the gliding posterior piece 

 would just tonch Avith its anterior end the edge of a piece of 

 food, it gave no reaction. This same arrangement Avith a 

 normal worm practically never fails to call forth the positive 

 reaction and bring the worm up on to the food. Posterior 

 pieces placed gently on pieces of food material do not extrnde 

 the pharynx and start feeding, but immediately glide down 

 from it and over the bottom of the dish. These experiments 

 with posterior pieces have been tried many times and under 

 varied conditions, in the hope that some sort of positive 

 results might be obtained, but never with success. This is 

 true for three daj^s after the operation. After a new head 

 has been fairly well formed the animal will react to food 

 again. The behaviour of one of these posterior pieces on 

 touching with the anterior end a piece of food is very 

 strikingly different from that of a normal animal. The cut 

 piece, if it touches with the front or sides of the anterior end 

 the smallest shred of food material, or any other substance, 

 gives a well-marked negative reaction, and goes in a new 

 direction away from the obstruction. It does not, as a rule, 

 crawl up over anything which it meets squarel}' " head-on," 

 but instead turns away. 



Thinking that possibly the pharynx might play a more or 

 less independent part in the normal food reaction, i. e., that 

 it might liave a set of reflexes of its own, not determined by 

 the rest of the body, I tried experiments with the isolated 

 pharynx removed entire from the body. Such an isolated 

 })harynx will remain alive for a considerable period, and 

 respond to stimulation. When first removed from the body 



' Bardeen (: 01, a) lias sliowu tliat it the transverse cut is in the region in 

 front of tlie eyes the posterior piece (comprising in this case nearly tiie whole 

 worm) will react norniiilly to food. 



