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CHAPTER II. 



THE MECHANICAL FUNCTIONS IN ZOOPHYTES. 



§ 1. General Observations, 



The mechanism of an organized being is designed to 

 fulfil various important objects. These we may distinguish 

 into two classes; the one having reference to its internal 

 welfare, the other to its relations with external bodies. The 

 diflferent parts of its system must, in the first place, be me- 

 chanically united and supported, as well as protected from 

 injurious external impressions; and they must at the same 

 time be so constructed as to admit of all the internal move- 

 ments, which the performance of their functions renders 

 necessary. They must, in the second place, be made capa- 

 ble of exerting upon external matter the actions which con- 

 duce to their well being; and, in order to enlarge their 

 sphere of action, they must have the power of transferring 

 the whole body from one place to another; or, in other 

 words, of effecting its progressive motion. 

 ' The objects included in the first of these branches of the 

 mechanical functions are answered by the organization both 

 of the vegetable and the animal systems: but those of the 

 latter belong exclusively to the functions of animal life. 

 The power of locomotion, more especially, constitutes the 

 most general and palpable feature of distinction between 

 these two classes of beings. A plant, during the whole pe- 

 riod of its existence, is fixed to the spot where it was first 

 produced, and is dependent for the continuance of its life on 

 local circumstances; such as the nature of the soil in which 

 its roots are embedded, and the qualities of the air and wa- 



