STUDIES ON SPATHIDIUM SPATHULA 199 



distance. The behavior of Spathidium differs markedly under 

 these two conditions. 



If the prey is instantly paralyzed it frequently remains against 

 the oral region of its captor and the reactions of the latter are 

 then relatively simple. The stimulus afforded by the contact 

 immediately stops the forward movements of the Spathidium, 

 which gives a few rapidly repeated avoiding reactions that 

 tend to keep it at or near the spot where the capture was made. 

 Meanwhile, the prey is moved around, apparently as a result of 

 the combined activity of the longer oral ciha and the gradually 

 expanding edges of the truncated end of the Spathidium, until 

 it may conveniently be encircled. This process of mouthing 

 successfully accomplished, nothing further is visible except the 

 gradual sinking of the prey through the greatly expanded cy- 

 tostome of the captor into the endoplasm (figs. 17, 18, and 19). 

 From the point of ingestion the course of the food vacuole within 

 the cell may be readily followed, especially when the prey has 

 pre\iously been fed with powdered carmine (cf. figs. 1 to 8). 

 The whole process from contact to complete ingestion takes 

 place in about thirty seconds, and the Spathidium, which usually 

 sinks to the bottom during the process, within a few seconds 

 more resumes its active foraging. Three such captures have been 

 observed to occur within eight minutes. Even certain conditions 

 which must be considered as highly abnormal apparently inter- 

 fere not at all with food taking. For example, a Spathidium 

 transfixed to a cover-glass with the needle of a Barber microdissec- 

 tion apparatus will paralyze a Colpidium and swallow it, pro- 

 vided, of course, the latter remains in contact with the mouth of 

 the Spathidium. 



Although the behavior of Spathidium is characteristic and re- 

 markable when it makes a direct capture, the most interesting 

 and significant cases are those in w^hich either the prey is not 

 instantly paralyzed, so that it moves a short distance away, 

 or, though rendered motionless, becomes removed from the oral 

 region of the Spathidium. Under these circumstances, the fac- 

 tors involved obviously become highly complex and the behavior 

 of the Spathidium is not identical in any two cases. The study 



