6io LIFE : OUTLINES OF GENERAL BIOLOGY 



of dissolved carbon dioxide. In every case there were two apparent 

 avenues of escape, one actually leading to freedom, the other ending 

 in a cul-de-sac, so that a choice of this avenue brought no relief. In 

 some cases the "unpleasant" result of making the wrong choice was 

 made more emphatic by the administration of an electric shock, or 

 by some other means. In most of the experiments the apparatus 

 was a Y-shaped arrangement, the animal being placed in the stem 

 of the Y, and having to make a choice between the left-hand or 

 right-hand branch of the Y when it arrived at the bifurcation. 



A dozen experiments with the water-fleas, involving altogether 

 1,400 lessons (the longest in any one experiment being 300), failed 

 to disclose any power of learning by experience. The proportion of 

 right to wrong choices showed no tendency to increase as the 

 experiments proceeded. In the experiment in which one water- 

 flea was given 300 trials or lessons, extending over eleven days, 

 there were fewer correct choices in the last quarter of the experiment 

 than in any of the other quarters. 



Twenty principal experiments were made with the water-mites, 

 the number of trials varying from 100 to 800, with a total of over 

 5.000. The first few experiments appeared to give positive results; 

 but further tests, undertaken to confirm this, showed that while the 

 water-mites have a well-marked tendency to form violor habits 

 (tending to run for a long series of trials into the same passage), 

 there was no good evidence of a power of learning. Some showed 

 improvement during the course of the experiment, but others 

 showed the reverse. 



Very different results were obtained by similar experiments on 

 young crayfish, for they very soon learned to avoid the wrong passage 

 and take the right one. In one experiment, in which entry into the 

 wrong passage, besides failing to bring freedom, resulted in an 

 electric shock, the animal took the wrong (left) turn at its first trial, 

 and then chose the right passage seven consecutive times. The 

 electrodes were then put into the right-hand passage. The crayfish 

 continued to go into this passage for 8 more times, receiving a 

 shock each time. In the next 21 times it only twice entered this 

 passage, making the correct choice in the other nineteen. 



The interpretation Prof. Agar gives of the difference in educa- 

 bility between the crayfish and the other two animals is instructive. 

 The difference may be correlated with the mode of life, for the 

 crayfish searches for its food with sense-organs which are susceptible 

 to stimuli from a distance. Having found its booty, it manipulates 

 it with its mandibles and maxilla;. It will also defend itself with its 

 great claws, and probably attacks other animals that might serve 

 it as food. "Daphnia lives a life of far less initiative. It feeds on 

 microscopic organisms, which are collected by a current of water 

 produced by the movement of certain of its appendages. Presumably 



