BY THOS. STEEL. 571 



In those land planarians possessing more than two eyes, these 

 organs are usually very numerous, amounting in some cases to 

 several hundred. They consist of minute black dots, only 

 occasionally sufficiently large to be visible to the naked eye, 

 extending in a single row round the edge of the anterior tip 

 usually expanding into a more or less crowded group on each 

 side just behind the tip, and then thinning out again to a single 

 row on either side which may extend right down to the posterior 

 end. In some species there is little or no side grouping, the eyes 

 being arranged in a single row extending backwards to a variable 

 distance. Those planarians possessing two eyes only (Rltyndiode- 

 mus, etc.), have them situated one on each side, just behind the 

 anterior tip. The eyes appear to be merely sense organs serving 

 to distinguish light from darkness, thereby enabling the animal 

 to avoid the light when it so desires. I do not believe that the 

 eyes possess &nj degree of true vision in the sense of enabling the 

 planarians to distinguish objects. 



As pointed out by Dendy (10, p. 42) the eyes may be well dis- 

 played by crushing the anterior tip of a living specimen between 

 a glass slip and coverglass, and examining under the microscope. 

 Small or young individuals may also be prepared by soaking in 

 oil of cloves, after previous preparation in strong spirit, when 

 they become translucent, and when mounted in Canada balsam 

 show the eyes to great advantage, besides giving an excellent 

 view of the alimentary canal and some other interesting details 

 of structure. 



When moving about they hold up the anterior end, curving 

 the sides downwards so that a cross-section would have the out- 

 line of a horseshoe, and delicately sweep the tip about, gently 

 touching any objects that may be in the way. If a small article 

 dipped in weak spirit, or the finger be held near the tip, they 

 become aware of its presence without coming in contact with it, 

 and quickly turn away so as to avoid it. Doubtless the ciliated 

 pits situated in a row beneath the eyes at this part, serve, as 

 suggested by different observers (3, p. 145; 8, p. 44), as olfactory 



