98 S. O. MAST. 



of vitality than feebly to beat the water with its vibratile cilia ; 

 on every side of it the darts lie scattered that were used to strike 

 it. Its enemy then approaches and quickly thrusts forth from its 

 mouth an organ shaped like a' tongue, relatively long and resemb- 

 ling a transparent cylindrical rod ; the free extended extremity of 

 this rod it fastens upon some part of the Paramecium's body. 

 The latter is then gradually brought near by the recession of this 

 tongue-shaped organ towards the buccal aperture of the Didinium, 

 which opens wide, assuming the shape of a vast funnel in which 

 the prey is swallowed up." 



Thon (1905, p. 294) maintains that the Paramecia are not 

 killed by trichocysts but by the seizing organ : " Das erste was wir 

 bei der Verfolgung des Didinium manovers konstatieren konnen, 

 ist, dass die Abtotung des Paramaecium nicht durch ' Tricho- 

 cysten ' sondern durch den mittleren Strang bewirkt wird. 

 Das lebhaft rotierende Didinium tastet mit dem Rande des Mund 

 offnung an den herumschwimmenden Paramaecium umher. 

 Plotzlich schiesst es durch eine energische Kontraktion des 

 Pharynx mit wunderbarer Geschwindigkeit den mittleren Strang 

 hervor, welcher dann aus der Mund offnung wie ein schlanker, 

 heller Cylinder heraus ragt und manchmal 2/3 Korperlange 

 erreicht. Dieser Strang wird nun in den Paramaeciumkorper sehr 

 fest eingebohrt und fiihrt den plotzlichen Tod des Paramaecium 

 herbei." 



Thon is undoubtedly correct in his statement that the Paramecia 

 are not killed by trichocysts. As a matter of fact, Didinium 

 discharges none. The mass of trichocysts seen after a Parame- 

 cinin is captured by a Didinium all come from the Paramecium, 

 and not from the Didinium as Balbiani and Maupas assumed. 

 This can be readily demonstrated by feeding the Didinia organ- 

 isms which have no trichocysts, e. g., Colpoda or Colpidium. I 

 have repeatedly seen these protozoa captured and swallowed by 

 Didinia but never saw trichocysts discharged during the process. 

 Are the Paramecia really poisoned by the seizing organ and sud- 

 denly killed as Thon states, and is this organ actually thrust out to 

 seize the prey? 



Didinia are powerful swimmers. If one becomes fastened to a 

 Paramecium even twice its own size, then the Paramecium at once 



