94 



Chapter V. 



Nutrition in the higher orders of Animals. 



In proportion as we rise in the animal scale, we 

 find that the operations of Nutrition become still 

 farther multiplied, and that the organs which per- 

 form them are more numerous, and more compli- 

 cated in their structure. The long series of pro- 

 cesses requisite for the perfect elaboration of nutri- 

 ment, is divided into different stages ; each process 

 is the work of a separate apparatus, and requires 

 the influence of different agents. We no longer 

 find that extreme simplicity which we noticed as 

 so remarkable in the Hydra and the Medusa, where 

 the same cavity performs at once the functions of 

 the stomach and of the heart. The manufacture 

 of nutriment, if we may so express it, is, in these 

 lower zoophytes, conducted on a small scale, by 

 less refined methods, and with the strictest economy 

 of means : the apparatus is the simplest, the agents 

 the fewest possible, and many different operations 

 are carried on in one and the same place. 



As we follow the extension of the plan in more 

 elevated stages of organic developement, we find a 

 further division of labour introduced. Of this we 

 have already seen the commencement in the multi- 

 plication of the digesting cavities of the Leech and 

 other Annelida ; but, in animals which occupy a 

 still higher rank, we observe a more complete sepa- 

 ration of offices, and a still greater complication of 



