PLANARIA ARETHUSA. 95 



Therefore I sought the upper orifice or 

 mouth, but in vain. 



It cannot fail to ^tcite the surprise of in- 

 telligent observers, that any difficulty should 

 attend a matter of such incontrovertible sim- 

 plicity as seeking the position of the mouth 

 of an animal, of that organ which must be 

 constantly in action for the very preservation 

 of life ; in one also where minuteness is no 

 obstacle to discovery. But, so great is the 

 diversity between most of those familiar to 

 our notice, and others more rarely the sub- 

 ject of contemplation, that the arrange- 

 ments of nature seem purposely calculated 

 to bewilder our acutest judgment. 



All planariae immediately become sensi- 

 ble of the vicinity of food, though whether 

 by means of vision, may be disputed. Their 

 motions then displayed, certainly have ra- 

 ther an opposite tendency ; and hence the 

 likelihood of an olfactory power resident in 

 them, such as may be peculiar to other ani- 

 mals not receiving the immediate rays of 

 light. Nearly a month subsequent to the 



