10 A Guide to the Zoological Collections in the 



and Sphxrozoum, Chilomonas, Paramcecium, 

 and Gregarina^ for an account of all of which 

 the visitor is referred to works on systematic 

 zoology. 

 The last exhibit is (V) a specimen of Eozoon canadense 

 from Canada, presented by Lady Dufferin. Eozoon has 

 been supposed to be the fossil remains of a gigantic Fora- 

 minifer, and its interest lies in the fact that, if fossil, it re- 

 presents, geologically speaking, the most ancient form of 

 life known to us. It is not generally conceded, however, 

 that Eozoon represents an organic structure. 



METAZOA. 



We next come to the Metazoa^ or animals that consist 

 of a complex of cells. 



Among the Protozoa the single simple cell performs, 

 though imperfectly, all the various functions by which 

 life is maintained : it receives simple impressions from 

 without, e.g. of the proximity of food, it is locomotive, 

 it takes hold of and digests prey, it respires, it circulates 

 its assimilated nutriment, and it excretes its useless waste, — 

 and in most of the Protozoa it does all this with any and 

 every part of its simple unicellular body. 



But when a multitude of cells is incorporated together 

 to form a large many-celled animal, it is not economical 

 for the incorporation that each of its cell-units should, so to 

 speak, go its own way and continue to perform all its func- 

 tions independently for itself. It is more economical, 

 both for the incorporation as a whole, and for each of these 

 cell-units, that each of the functions requisite for the com- 

 mon weal should be assigned to particular groups of cells — 

 to some groups the receiving of impressions, to other 

 groups the functions of digestion and assimilation, and so 



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