48 DEFINITION OF A PLANT. [LECT. II. 



organized substance. If these observations be 

 just, the remark of M. Mirbel cannot serve as the 

 means of distinguishing animals from vegetables ; 

 or of forming a correct definition of a plant. 



The most satisfactory opinion I have met with 

 on this subject is that supported by Dr. Alston, 

 who was Professor of Botany at Edinburgh about 

 fifty years since, and who appears to have received 

 the idea from Boerhaave. He makes the distin- 

 guishing characteristic of vegetables to consist in 

 the want of an internal stomach, animals being 

 nourished by their internal, and plants by their 

 external surface. It is extremely difficult to find 

 any thing like an exception to this opinion ; nor 

 do we think that the proofs of it fail with respect 

 even to the Polypus, whose construction is so 

 simple, that it may be turned inside out like a 

 glove, without disturbing its ordinary functions *.. 

 Polypi seize insects that come near them with 

 feelers, which they spread out in the water, and 

 convey them by this means to their mouths ; and, 

 as their internal cavity may be regarded as one 

 entire stomach, the food is passed rapidly through 



* It may not, perhaps, be unnecessary to observe, that a 

 Polypus is an aquatic animal, resembling in form the finger of 

 a glove, and, in structure, appearing to be made of particles 

 set in a gluey substance. Like those plants which can be slipped, 

 a Polypus may be cut into any number of pieces, and each di- 

 . vided portion become a new Polypus, a distinct animal. 



