198 LORANDE LOSS WOODRUFF AND HOPE SPENCER 



rapidly. In addition, the narrow anterior end is quite flexible, 

 and this makes the behavior still more complex. 



A careful analysis of the reactions of Spathidium to various 

 stimuli reveals quite clearly that in general its beha\'ior can be 

 interpreted in accordance with the 'avoiding reaction' as worked 

 out for various Protozoa by Jennings. In most cases when a 

 Spathidium, which is swimming forw^ard, is stimulated, it reverses 

 the effective stroke of the cilia, moves back for a short distance, 

 turns toward the side with the shorter anterior tip, and then 

 proceeds forward again on a shghtly different course. So far 

 its behavior appears quite stereotyped. But not so when the 

 anterior end strikes a small ciliate. Spathidium now exhibits 

 a series of reactions which may well be fundamentally of the same 

 nature as its others, since Spathidium is hmited, of course, by 

 the means at its command, but no good purpose will be served 

 by attempting to interpret it in the same terms. 



A casual survey of a number of hungry Spathidia swimming 

 among Colpidia gives one the impression that the Spathidia 

 chase their prey as one tiny ciliate after another falls victim 

 to the carnivores — one of the most spectacular sights in the world 

 of the Infusoria. But a careful study soon makes it clear that 

 the captures are the result of the chance contact of the oral region 

 of a Spathidium with a small ciliate. Indeed, when attempting 

 to follow the movements of a single Spathidium through a heavy 

 culture of Colpidia in order to study the details of the swallowing 

 process, one is frequently astounded to find how easily they miss 

 their prey ! Nothing happens unless the quarry strikes the anterior 

 end of the Spathidium nearly or quite in the center. Touching 

 the edges produces no effect on either animal. 



But when a Colpidium or similar cihate is fairly hit, the 

 picture changes instantly with respect to both of the animals 

 involved. The prey, which up to this moment was swimming 

 rapidly, usually instantly becomes motionless and quickly shows 

 pathological changes involving vacuolization of the cytoplasm 

 and disintegration of the cilia. Sometimes, however, paralysis 

 and death are not quite so rapid, and under these conditions the 

 quarry appears to tremble and moves haltingly away for a short 



