62 W. H. TALIAFERRO 
In the paper mentioned above, Hesse (’97) carried out similar 
experiments on Planaria gonocephala and obtained results which 
agreed with Loeb’s work on Planaria torva, namely, that decapi- 
tated worms gave the same reactions to light as normal ones 
except that the reactions required more time. 
Parker and Burnett (00) made a much more comprehensive 
and thorough study of the same question, using more accurate 
methods and treating the results statistically. They used in 
their experiments Planaria gonocephala, and confirm in the main 
the results obtained by previous investigators both as regards 
the reactions of decapitated worms and the time required for 
such reactions. 
In experiments on regeneration in Dendrocoelum lacteum, 
Lillie (’01) found, in harmony with the results obtained by Loeb 
in the polyclad Thysanozoén, that posterior headless pieces of 
this turbellarian do not react to light like normal specimens. 
He also maintains that any piece of a specimen of Dendrocoelum 
lacteum which is incapable of regeneration is, after a day or so, 
incapable of giving the normal responses to light. 
Mast (10), in a preliminary account of some experiments on 
a marine turbellarian, probably a triclad, found that these ani- 
mals orient fairly precisely to a horizontal beam of light, but 
that they do not orient after the eyes have been removed by 
gouging them out with a scalpel. 
From this short survey of the literature, we see that while 
the various descriptions of the structure of the turbellarian eye 
agree in all major details, the results of the work on the function 
of such eyes are so conflicting that it is almost impossible to 
draw any definite conclusions. The work of Loeb (’94) on 
Planaria torva, Hesse (’97) on Planaria gonocephala, and Parker 
and Burnett (00) on the same form, indicates that the removal 
of the eyes affects the reactions to light very little except to 
make the reactions slower. Opposed to these results, the work 
of Loeb (’94) on Thysanozo6én brochii, Lillie (’01) on Dendro- 
coelum lactum, and Mast (’10) on a marine form indicates that 
removal of the eyes results in the loss of the typical reactions 
to light. In all of this work, however, with the possible exception 
