174 



BEHAVIOR OF THE LOWER ORGANISMS 



m 







The stimuli with which we have thus far dealt are not directly in- 

 jurious, and do not interfere in the long run with the normal functions 

 of the organism, so that the power of becoming accustomed to them 

 and ceasing to react is useful. Let us now examine the behavior under 

 conditions which are harmless when acting for a short time, but which, 

 when continued, do interfere with the normal functions. Such condi- 

 tions rriay be produced by bringing a large quantity of fine particles, 

 such as India ink or carmine, by means of a capillary pipette, into the 

 water currents which are carried to the disk of Stentor (Fig. in). 



Under these circumstances the normal movements are at first not 

 changed. The particles of carmine are taken into the pouch and into 



the mouth, whence they pass into the internal 

 protoplasm. If the cloud of particles is very 

 dense, or if it is accompanied by a slight chem- 

 ical stimulus, as is usually the case with the 

 carmine grains, this behavior lasts but a short 

 time; then a definite reaction supervenes. 

 The animal bends to one side — always, in 

 the case of Stentor, toward the aboral side. 

 It thus as a rule avoids the cloud of particles, 

 unless the latter is very large. This simple 

 method of reaction turns out to be more 

 effective in getting rid of stimuli of all sorts 

 than might be expected. If the first reaction 

 is not successful, it is usually repeated one or 

 more times. This reaction corresponds closely 

 with the "avoiding reaction" of free-swim- 

 ming infusoria, and like the latter, is usually 

 accompanied by revolution on the long axis, 

 — the animal twisting on its stalk two or three 

 times as it bends toward the aboral side. 

 Fig. in.— A cloud of car- If the repeated turning toward one side 



mine is introduced into the water , ,. ■, . , . . 



currents passing to the mouth does not relieve the animal, so that the parti - 

 of stentor. c [ es f carmine continue to come in a dense 



cloud, another reaction is tried. The ciliary movement is , suddenly 

 reversed in direction, so that the particles against the disk and in the 

 pouch are thrown off. The water current is driven away from the 

 disk instead of toward it. This lasts but an instant, then the current 

 is continued in the usual way. If the particles continue to come, the 

 reversal is repeated two or three times in rapid succession. If this 

 fails to relieve the organism, the next reaction — contraction — usually 

 supervenes. 



