REACTIONS OF DIDINIUM NASUTUM. IOI 



A. M., June 10, there were three in each watch glass. One of 

 the animals had therefore divided. All appeared nearly normal 

 in form, the bulges and depressions due to the wounds having 

 almost disappeared. At 3:00 P. M., June n, all in the glass 

 that originally had three were dead, but each of those in the other 

 had divided so that there were now six in the dish that originally 

 had two. 



All of these observations show very clearly that Paramccium 

 is not immediately paralyzed by Didinium, as is generally sup- 

 posed, and that if there is any poison injected by the seizing organ, 

 it is very mild. There are also other organisms which show 

 no indication of immediate paralysis after an attack by this 

 ciliate. Two of these, Colpoda and Frontonia, were studied in 

 detail. These protoza appear to have an ectosarc which is not 

 as tough as that of Paramecium, so that after the seizing organ 

 is fastened to it and the Didiniwn suddenly reverses its directions 

 of motion and jerks back, as it usually does when it swims 

 against an object, the ectosarc frequently gives way and 

 the enemy swims off with a small mass of protoplasm attached to 

 the seizing organ. Sometimes, however, especially in the case 

 of Colpoda, the ectosarc does not break until the Didinium has 

 drawn the victim part way in and the mouth begins to close. 

 Thus I have seen specimens of Colpoda escape, and recover, after 

 having had various portions, even as much as one third of the 

 body, torn away. And in case these creatures do not escape but 

 are swallowed, the cilia can be seen to beat as long as any part 

 projects. 



Frontonia is one of the largest of the protozoa. It is much 

 larger than Paramecium, but it is nevertheless, vigorously 

 attacked by Didiniwn. The seizing organ readily sticks to the 

 surface of this creature, but the ectosarc almost always gives way 

 as soon as the Didinium jerks back after striking it. This is no 

 doubt due, in part at least, to the relatively great momentum of 

 this animal. It takes a much greater force to move Frontonia 

 than it does to move Colpoda, so that there is a much greater 

 strain on the ectosarc of the former than there is on that of the 

 latter when a Didinium suddenly reverses the direction of motion 

 after the seizing organ is attached. Thus the creature attacked 



