OX THE GROUP PROTOZOA. 41 



so far back as 1851, the existence of true ova was conclusively demon- 

 strated in the genus Tethya. 



Those who refuse to admit the Protozoa within the animal kingdom 

 are bound legitimately to solve the question which they have raised as 

 to their true systematic position. Professor Agassiz, as we have seen, 

 adopts the ready expedient of banishing the majority of the group to 

 the vegetable kingdom. Botanists, however, refuse to acknowledge the 

 outcasts thus summarily thrust upon them for protection. Our great 

 anatomist, Professor Owen, has proposed to cut short the difficulty, by 

 establishing for their reception a third primary division of the organic 

 world. By him we are informed that — 



" The two divisions of organisms called ' plants' and ' animals' are specialized mem- 

 bers of the great natural group of living things; and there are numerous beings, mostly 

 of minute size, and retaining the form of nucleated cells, which manifest the common 

 organic characters, but without the distinctive super-additions of plants and animals. 

 Such organisms are called ' Protozoa,' and include the Sponges or Amorphozoa, the Fo- 

 raminifera or Rhizopods, the Polycystinese, the Diatomaceae, Desmidias, Gregarina, and 

 most of the so-called Polygastria of Ehrenberg, or infusorial animalcules of older 

 authors." 



The " common organic characters" here alluded to have, in a pre- 

 ceding paragraph been denned as follows : — 



"Organisms, or living things, are those which possess such an internal cellular or 

 cellulo- vascular structure as can receive fluid matter from without, alter its nature, and 

 add it to the alterative structure. Such fluid matter is called ' nutritive,' and the actions 

 which make it so are called 'assimilation' and 'intra-susception.' These actions are 

 classed as 4 vital,' because, as long as they are continued, tbe ' organism' is said ' to 

 live.'" 



Professor Owen then goes on to distinguish between plants and ani- 

 mals thus . — 



" When the organism can also move, when it receives the nutritive matter by a 

 mouth, inhales oxygen, and exhales carbonic acid, and developes tissues, the proximate 

 principles of which are quaternary compounds of carbon, hydrogen, oxygen, and nitro- 

 gen, it is called an 'animal.' When the organism is rooted, has neither mouth nor sto- 

 mach, exhales oxygen, and has tissues composed of ' cellulose' or of binary or ternary 

 compounds, it is called a ' plant.' " 



To do justice to these definitions, we shall, without alteration of the 

 author's language, present them in the form of the four following pro- 

 positions: — 



1 . The animal can move ; the plant is rooted. 



2. The animal receives nutritive matter by a mouth ; the plant has 

 neither mouth nor stomach. 



3. The animal inhales oxygen, and exhales carbonic acid ; the plant 

 exhales oxygen. 



4. The animal developes tissues, the proximate principles of which 

 are quaternary compounds of carbon, hydrogen, oxygen, and nitrogen ; 



vol. i. — x. H. E. G 



