REACTIONS TO LIGHT IN PLANARIA MACULATA 101 
These results lend very strong support to the conclusions reached 
in the section dealing with the localization of sensory regions in 
the eye. In fact, they practically prove the conclusions in regard 
to one region of the eye. 
As an argument against the conclusions set forth above, it 
might be asked if the removal of the posterior region of the eye 
has not injured the remainder of the organ to such an extent 
that we are really dealing with an animal that has no eyes at 
all. In answer to this question it can be said, 1) the sections 
of such animals reveal no indication of any injury to the remain- 
ing rhabdomes and, 2) the remainder of the rhabdomes are still 
functional. By referring to the description of the reactions of 
such animals, it is very evident that the last statement is correct, 
for it will be remembered that if the animal wanders away from 
the side containing part of the eye, it sharply and accurately 
orients as soon as the light illuminates the eye from a lateral 
position. The only plausible explanation of this is that the 
reaction follows from an illumination of the rhabdomes in the 
center of the pigment-cup, or, in other words, that removing 
the posterior portion of the eye did not injure the capacity of 
the remainder to function. — 
3. Reactions to light in specimens with one eye and the anterior 
half of the other eye removed. The attempt was made to carry 
out experiments similar to those described in the preceding 
section, using, however, specimens possessing only the posterior 
half of one eye instead of the anterior half. 
All specimens with one eye and the anterior half of the other 
(remaining eye) removed react precisely as do specimens with 
both eyes removed. Under no circumstances is illumination 
of the part of the eye remaining in the animal followed by orien- 
tation as was the case in the animals with the posterior half of 
the eye removed. ‘The results, at first, seemed rather puzzling, 
but it can be seen by referring to the section on the structure of 
the eye that the nerve processes from all of the rhabdomes leave 
the eye from the anterior edge, and histological examination 
showed that all of these were cut in removing the anterior half. 
Removal of the posterior half of the eye, on the other hand, did 
not injure these fibers. 
