ZOOLOGICAL CLASSIFICATION 



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THE limits of the Animal Kingdom are still undecided, and it is 

 probable that no absolute division between animals and plants 

 exists. The thin membrane of the animal cell, when present, 

 has been contrasted with the thicker and harder membrane of 

 the vegetable cell, in the former case admitting solid particles of 

 food into the body, as well as enabling it to combine to form the 

 fibrous tissues, which the vegetable cell is unable to do. But it 

 is doubtful if any such hard-and-fast line can be drawn between 

 them. 



To evade the difficulty and to exclude all doubtful organisms, 

 Hackel proposes to form an intermediate kingdom, Protista, 

 including Protozoa and the lower plant-forms Labyrinthulea>, 

 Diatomaceae, and Myzomycetes, to which he seems inclined to 

 add the Fungi. But already, in 1859, Owen (Encycl. Brit.) 

 introduced a " kingdom " Protozoa [this name was first proposed 

 by Siebold], including Diatomacese &c., which he placed before 

 the " kingdom Animalia ; " and John Hogg, the year after, pro- 

 posed the term " Protoctista" for a " Prirnig 'enal kingdom," con- 

 taining both Protophyta and Protozoa. The latter are, however, 

 undoubtedly animal organisms; and in any case the limitation 

 will be an arbitrary one. 



It is now considered almost without exception that there are 



