184 LECTURE IV. 



tciinly of our knowledge with regard to the 

 nourishment of this and some other ani- 

 mals. 



With such exceptions, all other animals 

 have a digesting cavity, and the lowest 

 orders appear to have no other organs, the 

 whole interior being stomach, and the whole 

 animal forming only the walls by which it 

 is surrounded and supported, as is exem- 

 plified in actinise and medusas. Mr. Hun- 

 ter, in his M.S. of they year 1776, writes 

 as follows : " The apparatus necessary lor 

 digestion is as simple as any thing we can 

 well conceive. It only requires a bag or 

 cavity fit to contain the substance to be 

 digested, joined with the power of furnish- 

 ing the fluid capable of digesting the said 

 substance. It is therefore to be considered 

 as a gland and a cavity. Indeed, it is ne- 

 cessary, that another apparatus should be 

 added ; a system for absorbing the digested 

 food and nourishing the bag, as well as 

 preparing the fluid it secretes." Before 

 this time, Mr. Hunter had injected the ves- 

 sels of medusee from the stomach with co- 



