64 



J. M. D. OLMSTED 



the extent of regeneration of the nervous system, it was found 

 that each half of the brain remained in each piece exactly as it 

 was at first (figs. 6 and 7). In no case was a portion of the brain 

 able to restore the missing nervous tissue. 



<:iJv- 





; • • 



8 9 



Fig. 6 Eyes and brain of worm shown in figure 4. 



Fig. 7 Eyes and brain of worm shown in figure 5. 



Fig. 8 Normal eyes and brain of P. littoricola for comparison. 



Fig. 9 Eyes of P. littoricola four weeks after removing the brain. Broken 

 line indicates the extent of new tissue. Tendency toward normal grouping of 

 eyes is marked even in absence of brain. 



To make more certain that these polyclads were unable to 

 regenerate a brain, a small disc just large enough to include the 

 brain was cut from the w^orm by means of a thin-walled glass 

 tube. In many cases the anterior margin of the hole left in the 



