REACTIONS OF DIDINIUM NASUTUM. 103 



den nach Mallory behandelten Praparaten. Sobald dem Para- 

 maecium die Wunde verursacht wird, fangen in der nachsten 

 Umgebung sich zahlreiche Vacuolen zu bilden an, die manchmal 

 eine ansehnliche grosse ereichen mid das Plasma quillt hervor." 

 There are then two sources of evidence in favor of the view 

 that noxious fluid is injected by Didinium in capturing its prey, 

 the apparent sudden death of the prey and the vacuolation in 

 the neighborhood of the wound made by the seizing organ. 

 We have shown conclusively that paralysis is merely apparent, 

 that organisms are not as suddenly killed as they appear to be, 

 and that they frequently recover if they escape after being 

 wounded. The vacuolation can be conceived to be due to physical 

 effects quite as well as to toxic effects. At any rate it is 

 well known that a physical injury in Paramecium does cause 

 vacillation and that these organisms are often killed by slight 

 abrasions. It is almost impossible to obtain specimens which 

 have recovered after having a portion of the body cut off. 



Let us now proceed to the second question stated above. Does 

 Didinium thrust out the seizing organ in capturing its prey? 

 This question I shall consider in connection with the function of 

 trichocysts. 



FUNCTION OF THE TRICHOCYSTS. 



If a large number of Didinia which have been without food 

 for a few days are thrown into a solution containing numerous 

 Paramecia, many of them will begin to feed at once. If they are 

 now suddenly killed, it is not difficult to find specimens attached 

 to Paramecia with the seizing organ extended. If the Paramecia 

 are relatively small, it will be found to be extended only a short 

 distance, but if they are relatively large, one frequently finds it ex- 

 tended to a distance nearly equal to the length of the body of the 

 Didinia as represented in Fig. n. Balbiani and Thon also rep- 

 resent this organ thus extended. Both of these authors say that 

 it is thrust out. Thon (1905^.294) in describing the capture 

 of Paramecia says it is forced out by violent contraction with the 

 rapidity of lightning and later (p. 295), in referring to Didinium 

 feeding on flagellates, he writes : " Da konnen wir sehen dass 

 ein Didinium in kurzer Frist einiger Minuten eine grosse Zahl 



