BEGINNINGS OF CO-OPERATION 6l 



longer, which in each case are the grouped worms, 

 are given as lOO per cent, regardless of the time 

 taken; while the isolated worms, which had been 

 irradiated in the same dishes as their accompanying 

 groups, survived on an average of 78 per cent and 

 77 per cent respectively in the two tests with well 

 water, and only 61 per cent in the test in dis- 

 tilled water. The numbers between the blocks show 

 the number of worms averaged for each block; that 

 is, the number of pairs of worms for which results 

 are summarized. The statistical significance given 

 in terms of 'T" is very high in each case. 



The number present during exposure is impor- 

 tant, as well as the number present during the time 

 when it is being determined how long the animals 

 will survive. Such data are summarized in Figure 4, 

 which is built exactly on the same principle as that 

 preceding. Worms radiated when crowded (left-hand 

 block), and then tested when isolated, survived 517 

 minutes, while accompanying worms which had been 

 radiated singly as well as tested when isolated, lived 

 only 24 per cent as long. Those radiated in a group 

 and tested singly (middle block) lived 55 per cent as 

 long as those which had been radiated in a crowd 

 and then were isolated to observe the effects of radi- 

 ation. It will be remembered that these crowded 

 worms actually shaded each other and so gave 



