COMPLEX APPARATIJS FOR NUTRITION. 105 



plicated in their structure. The long series of 

 processes requisite for the perfect elaboration of 

 nutriment, 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, Avhere 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, con- 

 ducted upon 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 farther division of labour introduced. Of this 

 we have already seen the commencement 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 tp a much 

 greater extent than in the inferior departments 

 of the animal creation. Besides the stomach, or 

 receptacle for the unassimilated food, another 

 organ, the heart, is provided for the uniform dis- 



