6o THE SOCIAL LIFE OF ANIMALS 



quately controlled. Some of the things we have found 

 out are: 



If the worms are crowded under the ultra-violet 

 lamp so that they shade each other, the shaded ones 



RAOIATEO RADIATED RAOIATEO RADIATED 



enOUPEO 6R0UPEO GROUPED GROUPED 



reSTCO TESTED TESTED TESTED 



6R0UPEO SINGLY GROUPED SINGLY 



148* 



247' 



RADIATED RADIATED 



GROUPED GROUPED 



TESTED TESTED 



GROUPED SINGLY 



267' 



IH 168' 

 tI ItI 

 ooooojjj HH^oooooJUJ I 



137* 



140 ^M 

 P I 



aooo4jU 



WELL WATER 



DISTILLED WATER 



Fig. 3. Planarian worms which have been exposed to 

 ultra-violet radiation disintegrate more rapidly if isolated 

 than if grouped. 



are definitely protected. When such crowding is 

 eliminated and by constant watching and stirring, 

 if needed, during exposure, the worms are kept ap- 

 proximately equally spaced, even then the grouped 

 worms survive longer than if isolated. Some of the 

 relationships are shown in Figure 3. 



Each block represents the survival time of several 

 series of worms. The figures at the top of the block 

 give the average length of survival in minutes. The 

 blocks are constructed so that the worms surviving 



