356 STUDIES IN GENEEAL PHYSIOLOGY 



in plants also, but in the latter case through different 

 mechanisms. These facts which I considered as self-evident 

 have been misunderstood by one author and have been falsely 

 represented, as though I had asserted that brain and eyes 

 are superfluous. 



From what I said it also followed that in animals which 

 possess eyes the sensitiveness to light need not by any means 

 be limited to the eyes. Photosensitive elements may be 

 found also in other portions of the surface of the body. 

 Graber has in fact already reported experiments on Tritons 

 and angleworms which he claims point in the same direction. 

 It could, moreover, be foreseen 'that an effect of light might 

 perhaps be possible in many animals without the existence 

 of a true reflex arc, for I found in Ciona intestinalis that a 

 typical reflex phenomenon continues to exist in this animal 

 after destruction of the central nervous system. There was 

 finally the possibility also that both conditions might be 

 found together in the same animal. The latter is the case 

 in Planaria torva, determined to be such by Dr. Wheeler. 



4. After what has been said it is scarcely necessary to 

 emphasize the fact that brainless pieces of Planaria torva will 

 not assume the dorsal position any more than will uninjured 

 animals. All my experiments to bring about forced move- 

 ments in these animals through unilateral destruction of the 

 brain remain as fruitless as in Thysanozoon. 



III. EXPERIMENTS IN CEREBRATULUS MARGINATUS 



The Nemertines possess a more highly developed brain 

 than do the Planarians. The brain is larger and shows also a 

 greater subdivision into smaller parts. It also is continued 

 into two lateral nervous cords. The latter contain "a super- 

 ficial covering of ganglion cells which may give rise to 

 ganglion-like swellings at the points where the nerves 

 branch." 1 



1 CLAUS, Lehrbuch der Zoologie, 4. Aufl., p. 336. 



