IO4 S. O. MAST. 



von Flagellaten, welche nicht naher bestimmbar ist, einfangt. 

 Blitzschnell wird der Strang hervorgestiilpt, mit derselben Gesch- 

 windigkeit verschwindet der Flagellat im Innern des Feindes." 

 If this organ was actually shot out with lightning speed, as Thon 

 says, it is difficult to see how one could be certain of just what did 

 happen. 



I have studied the maneuvers of Didinium in capturing its prey, 

 many times with the greatest care, and was never able to see 

 any indication of such a thrusting out of the seizing organ. 

 What actually happens is this. The Didinia, especially when 

 hungry, swim about very rapidly. In such specimens the seizing 

 organ appears to be entirely withdrawn ; it cannot be seen to 

 project beyond the surrounding surface in the least. When one 

 of these rapidly moving creatures chances to swim against a 

 Parauiecinin, it strikes with such force that the Parameciwn 

 can clearly be seen to be pushed out of its course. This is partic- 

 ularly marked if the prey is small. There is no doubt but that 

 the distal end of the oral projection comes in close contact with 

 the surface. This I have actually observed many times. As 

 soon as the Didinium strikes an object, c. g., a Paramecium, it 

 usually suddenly stops rotating and at the same time reverses its 

 direction of motion. One can never tell whether the seizing 

 organ is fastened or not until this reversion takes place. It very 

 frequently happens that the organ does not become attached 

 during this process and then the Didinium, of course, fails to 

 capture its prey. Just why the seizing organ sticks to a Para- 

 mecium some times and not at others I am unable to explain. 

 All that can be seen in preparations which show the organ 

 fastened is small dots at the point of fusion represented in Fig. 6. 

 It may be that sometimes this organ is entirely withdrawn so 

 that when the hunter strikes a Parameciwn it does not actually 

 come in contact with the surface. 



If the seizing organ becomes fastened, either the fusion with 

 the surface or the pull exerted by the jerking back of the 

 Didinium immediately after the fusion produces some sort of 

 injury, for the Paramccinm at once responds by discharging a 

 great number of trichocysts from the ectosarc for some distance 

 around the point of injury, Fig. n. As soon as the trichocysts 



