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 perform them are more numerous 

 and more complicated in their structure. The long series 

 of processes 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 func- 

 tions of the stomach and of the heart. The manufacture of 

 nutriment, if we may so express it, is, in these lower zoo- 

 phytes, conducted upon a small scale, by less refined me- 

 thods, and with the strictest economy of means; the appara- 

 tus 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 development, we find a farther division of 

 labour introduced. Of this we have already seen the com- 

 mencement in the multiplication of the digesting cavities of 

 the Leech and other Annelida: but, in animals which occupy 

 a still higher rank, we observe a more complete separation 

 of offices, and a still greater complication of organs. The 

 principle of the division of labour is carried to a much great- 

 er extent than in the inferior departments of the animal 

 creation. Besides the stomach, or receptacle for the unas- 

 similated food, another organ, the heart, is provided for the 



