IO6 S. O. MAST. 



seizing organ, if any; but if the Didiniuni is small and the Para- 

 mecium large, this organ is frequently drawn out nearly the 

 length of the body, as stated above, and the protuberance of ecto- 

 sarc becomes so much extended that it breaks and the Paramecium 

 swims away, leaving the Didiniuni attached to the bit of ectosarc 

 imbedded in the mass of trichocysts (Fig. 12). It is remarkable 

 what a firm jelly-like consistency this mass has, and how securely 

 the bit of ectosarc pulled out of the Paramecium is imbedded 

 in it. The Didiniuni thus fastened to the mass of trichocysts at 

 first appears to be hopelessly entangled but it soon begins to 

 loosen itself by violently jerking backward and darting forward. 

 After it has thus become partly free it begins to rotate on the 

 longitudinal axis and soon twists the seizing organ off at a point 

 in the body some distance from the surface and swims away 

 leaving this important organ in the tangle of trichocysts as repre- 

 sented in Fig. 13. Sometimes the trichocysts give way and the 

 hunter escapes with the bit of protoplasm, which it then swallows. 

 In one such instance, however, which came under my observa- 

 tion, the Didiniuni turned suddenly immediately after it became 

 free, and swam violently against the slide on which it was 

 mounted. The bit of protoplasm adhered to this so firmly that it 

 held the creature fast and it escaped only after twisting the 

 seizing organ off. This illustrates in a striking way one of the 

 properties of bare living protoplasm. I am not positive as to 

 what becomes of these specimens without a seizing organ. They 

 appear normal in every respect and it is altogether likely that the 

 missing organ is regenerated in course of time. There is no 

 evidence that the trichocysts have a toxic effect on the Didinia, 

 or that they injure them in any way. They appear to function 

 merely by mechanically separating the prey from its enemy. 

 There are, however, two other factors which assist in this separa- 

 tion : (i) the violent struggle of the Paramecium after it is 

 attacked, and (2) the sudden reversion in the direction of motion 

 of the Didiniuni. That these two factors, however, are insuffi- 

 cient in themselves to break the connection or even to account 

 for the extreme extension of the seizing organ and the large pro- 

 tuberance in the ectosarc is evident from the fact that when a 

 Didiniuni attacks a Paramecium on a surface where the tricho- 



