EXPERIMENTS ON WORMS 



93 



crawl into them and will not leave them again. This 

 is due to stereotropism. If there are, for instance, 

 six such tubes in a vessel and six normal Nereis are 

 put into it, we may be sure that after a few hours 

 every Nereis will have established itself in a tube. It 



FIG. 29. A GROUP OF NEREIS WHOSE BRAINS HAVE BEEN REMOVED. THEY AT 

 LAST COLLECT IN A CORNER OF THE AQUARIUM AND PERISH IN THEIR VAIN 

 ATTEMPT TO Go THROUGH THE GLASS. (After Maxwell.) 



frequently occurs that a Nereis goes into a tube that 

 already has an occupant. In that case the new-comer 

 withdraws with a start as soon as it touches the old 

 occupant. As long as the new-comer is in pos- 

 session of its brain, it leaves the tube under such 



