'J'2 PLANARIA ARETHUSA. 



pale colour, selected from the rest, to the 

 microscope by candle light. Nothing re- 

 sembling eyes, stigmata, or marginal specks, 

 could be detected. At a future period, 

 however, on repeating the investigation by 

 day, two minute black specks were disco- 

 vered in the middle of the upper surface of 

 the neck, nearly in the same position as 

 they are to be seen in the planaria auriculata. 

 This is an observation, like some others on 

 animals which elude our controul, exceed- 

 ingly difficult to be accomplished, both from 

 the corporeal opacity and incessant motion 

 of the planariae ; and in those of dark co- 

 lour, it is scarce possible by any means to 

 obtain a view of the eyes. Whether they 

 are simple or compound, is not absolutely 

 certain. More probably each is a single 

 speck, deep sunk in an orbit or socket, 

 where perhaps it is susceptible of some 

 movement or alteration of figure. They 

 appeared differently in different observa- 

 tions. Both were not always of the same 

 shape ; frequently they resembled a cres- 



