STUDIES ON SPATHIDIUM SPATHULA 201 



also moves backward and forward in the neighborhood of its 

 prey. It is obvious, of course, that such reactions sooner or 

 later will again bring the mouth of the Spathidium in contact 

 with the food. But, a careful analysis of many cases clearly 

 shows that usually these stereotyped reactions are msufficient 

 to account for the comparative precision exhibited by the Spath- 

 idium in recovering its quarry. And further, the reactions of 

 the Spathidium are successively modified so that, although it may 

 have become removed several times its own length, within a 

 relatively short time the oral region again comes in direct con- 

 tact with the food, which is then engulfed in the manner pre- 

 viously described. This is a fact that we beheve is indisputable. 

 Of course, such a result as the above does not invariably occur; 

 sometunes the prey is never found again. But, when all the 

 complex factors involved are appreciated, it is remarkable how few 

 paralyzed ciliates are lost. 



A Colpidium before being paralyzed has no effect whatsoever 

 on Spathidium; after paralysis it appears to be a center of at- 

 traction, and not only to the Spathidium whose oral region it 

 touched, but also in a much less marked though significant 

 degree to other Spathidia in the immediate neighborhood. This 

 last observation naturally suggests the probable explanation. 

 Chemical substances excreted by the djTing organism, or secreted 

 at the tmie of contact by the captor itself, afford a stmiulus 

 which results in the characteristic behavior of Spathidium. It 

 is probable that the effective substance in question is secreted by 

 the Spathidium itself because the oral region of the latter is 

 frequently, especially after an unsuccessful capture, a stimulus 

 to neighboring specimens. And the same factor may well be 

 responsible for the peristomal fusion incident to conjugation. 

 Whatever the explanation may be, the point not to be lost sight 

 of is that Spathidium 'senses at a distance' its paralyzed prey. 



The reaction against the early anthropomorphic interpretations 

 of the behavior of the Infusoria resulted in a conception of the 

 simpler animals which almost left out of account the fact that 

 they are organisms. The study of Spathidium adds one more to 

 the body of data being rapidly brought to the fore that makes 



