48 PHILOSOPHY OF ZOOLOGCGY. 
cavity into which they empty their contents, or any en- 
largement which bears a resemblance to a stomach. In 
the inferior tribes of vegetables, the organs of nutrition ap- 
pear to be constructed according to the same model. In 
consequence of these peculiar arrangements, the absorbing 
vessels of nutrition in plants, arise on the surface; while 
those of animals originate on the inside of the alimentary 
canal. Dr Atston, who regarded this last character as 
constituting an obvious and essential mark of distinction 
between plants and animals, fancifully termed a plant an 
inverted animal *, 
In all animals, in which the intestinal canal is of suffi- 
cient size to be obvious to the senses, we perceive that 
crude matter is conveyed to it by the mouth; and that af- 
ter a certain time, the useless part is thrown out as excre- 
ment. In plants, all the food which enters their tubes, 
appears to be in a state of solution ; and all the superfluous 
quantity is dissipated im gaseous or aqueous exhalations. 
Some have attempted to insinuate, that plants can live 
on inorganic matter, while animals can be supported only 
on that which is or has been organized matter, either of a 
vegetable or animal nature +. A moment’s reflection, how- 
ever, on the similarity between the elementary substances, of 
which all organized bodies are composed, will not fail to 
induce us to assign to them a common origin. All the 
larger animals feed on the remains of animals and vege- 
tables, while the plants feed on the juices of the soil. But 
we are utterly ignorant of the particular state of combina- 
tion, in which the atoms of the nourishing substances may 

* “ Tirocinium Botanicum Edinburgense,” Edin. 8vo. 1753 ;—a work 
which may still be perused with advantage by the student of botany, 
+ Smitn’s Introduction to Botany, p. 5. 
