PLANARIA ARETHUSA. 87 



no delineation of it was obtained at the 

 time. I may just observe, that in figure, 

 colour, and position of the eyes, it seemed 

 closely allied to the Planaria auriculata of 

 MuUer, described and represented in the 

 Zoologia Danica, vol. ii. page 37. Plate 

 Ixviii. Figs. 16, 17. The latter, however, 

 was scarcely perceptible by the naked eye, 

 and an inhabitant of the sea; whereas mine 

 dwelt in fresh water, and nearly approach- 

 ed the former species in size. 



The sudden disappearance of animals 

 without any sensible cause, is not unexam- 

 pled. I have witnessed it myself among 

 the smaller tribes ; and the same is record- 

 ed by the most celebrated naturalists. There 

 are reiterated proofs that those of gigantic 

 proportions have become extinct ; and it is 

 probable that others are daily vanishing 

 from the surface of the earth, which none 

 excepting hybrids can be said to replace. 

 Several sources, equally effectual, may con- 

 tribute to the extirpation of animals ; the 

 preponderance of enemies, cessation of the 



