Q& PLANARIA ARETHUSA. 



preceding observation, several planariae of 

 the species at present described, were sup- 

 plied with the soft part of an oyster; a sub- 

 stance which they generally receive in pre- 

 ference to the fleshy parts of animals. Some 

 lighter particles floated at the surface, and 

 I saw, with infinite surprise, a planaria also 

 swimming supine in their vicinity, quickly 

 protrude a long, milk-white, tubular probos- 

 cis, by which they were greedily absorbed. 

 No wonder, indeed, that my search after 

 any analogous organ had been fruitless. 

 Unlike that of all other animals with which 

 it is allied, or which come within the sphere 

 of my knowledge, its aperture, instead of 

 belonging to the head, is in immediate 

 approximation to the tail. Situated in the 

 under surface, and towards the lower extre- 

 mity, it proves to be what naturalists have 

 so erroneously denominated the ventral 

 pore. Although this may be deemed a 

 trivial fact in the grand scale of observa- 

 tion, it impressively warns us to distrust 

 analogical reasoning for which we are ena- 



