THE COASTS OF SICILY. 275 



element, by its gradual development and modification, 

 would produce, according to circumstances, either 

 muscular fibres, the parenchyma of the glands, or the 

 matrix of the osseous tissue. According to the same 

 theory, the vessels are in like manner cells, which 

 being at first spherical, become gradually elongated, 

 until, combining together, they constitute by their 

 reunion the thousand vascular ramifications of the 

 body. 



This theory numbers amongst its partisans many 

 distinguished physiologists. It is certainly highly 

 attractive from its simplicity, and from the manner 

 in which it enables us to embrace all the phenomena 

 of development, while it establishes the existence of 

 ultimate relations between the two great divisions 

 of organised creation. A similar theory has indeed 

 been long adopted by botanists, who regard it as the 

 expression of all the facts to be observed in plants. 

 We have seen, however, that the case is different 

 with respect to animals, although here we believe 

 that the cellular theory furnishes several useful 

 results. It may be well adapted to guide us in the 

 study of certain animal tissues which present remote 

 relations to those of plants ; but when applied to the 

 entire animal kingdom, it can no longer be accepted 

 as true. 



We will add another example to those already 

 given. It had long been known that in the Ano- 

 donta — a species of fresh-water mussel, very common 

 in the neighbourhood of Paris — the heart is traversed 

 by the last portion of the intestine. M. Edwards, 

 moreover, in studying the organisation of the Pa- 



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