212 HARRY BEAL TORREY. 



Pollock ('82) observed this fact but was unable to reconcile his 

 varying results. The reason for his failure was, I believe, that 

 he failed to distinguish between general and local stimulation. 

 When the meat juices of the annelid used previously were dis- 

 charged gently over a polyp from a pipette, I observed that the 

 tentacles always waved inward, without regard for the direction 

 from which the juice was coming. This general chemical stimu- 

 lation produced the same response from the tentacles that a me- 

 chanical stimulation of the foot disk provoked. In both cases 

 then, in which the tentacles waved inward and away from the 

 flesh, the diffusion of soluble substances from the latter was 

 probably so rapid that the tentacles were stimulated on all sides 

 so nearly at the same time that no differential of stimulation 

 beween opposite sides of the tentacles was established, the neces- 

 sary condition of a directive reaction. But why the movement 

 toward the mouth ? Because it is the primitive clutching move- 

 ment already spoken of as most likely to capture food organisms, 

 in a polyp whose tentacles are habitually outstretched. It is the 

 simplest adaptation of the prehensile mechanism, common to 

 hydroids as well. 



The responses of the tentacles to mechanical and chemical 

 stimuli are essentially the same. The bend is toward the stimu- 

 lus when the stimulation is local, toward the mouth when it is 

 general, whether direct or indirect. 



If we turn now to the phenomena of swallowing, we shall see 

 that the cilia of both lips and oesophagus may respond to mechani- 

 cal as well as chemical stimulation by waving more strongly inward 

 than outward. I early observed that not only were pieces of 

 flesh occasionally rejected, but bits of shell and gravel were 

 sometimes taken in. With the idea in mind that the size and 

 shape of the object might affect the reaction, several substances, 

 presumably chemically inert, were given to various polyps, in 

 pieces varying in these respects. Pieces of very thin paper, from 

 i mm. to 3 mm. square, when placed npon the tentacles, were 

 cast off in half an hour. A piece of cork, about one fourth as large 

 as the polyp, was likewise rejected. A much smaller piece, 

 capable of being easily ingested, was taken into the gullet and 

 retained for thirty minutes. A piece of paraffine of similar 



