REACTIONS OF DIDINIUM NASUTUM. 



measure them with any degree of accuracy while alive, and if 

 they are killed before the swallowing process is complete, one 

 can never be certain that it could have been accomplished had 

 they not been killed. The simplest method seems to be, to fix a 

 large number of specimens immediately after they have been 

 feeding, then select the largest and calculate the relative size of 

 the organism swallowed. This was done and some specimens 

 were found in which the substance of the Parauiccium swallowed 

 occupied approximately ten times as much space as the substance 

 of the Didininm. In such specimens the Didirmini forms a mere 

 film over the Paramecium, as represented in Fig. 16. If other 

 animals could engulf objects relatively as large as this hunter 

 ciliate can, a common garter snake could readily swallow a rabbit, 

 a large house cat a sheep, and a lion or a human being a full 



grown ox. 



What are some of the factors involved in the process of swal- 

 lowing objects of such extraordinary size? 



Didinia attack their prey at any point with which they chance 

 to come in contact, and appear to be able to swallow them 

 equally well no matter whether they become attached to the 

 sides or the ends. If a Didiniwn succeeds in remaining attached 



...H 



FIG. 18. A Didinium showing a canal, c, formed by the invagination due 

 to the movement of the seizing organ, s, after the escape of a Colpoda 

 which had been partially swallowed, n, nucleus ; c.v., contractile vacuole. 



to its prey after it has made an attack, it at once begins to draw in 

 the seizing organ. This it can do, no matter how far the organ 

 has been extended by the discharge of trichocysts and other 

 factors. The captured prey is thus drawn to the mouth which 

 gradually opens and surrounds it, as the seizing organ travels 

 toward the posterior end of the animal. The whole process is 



