346 ANIMAL NATURE OF DIATOME^. 



species and genera, whether animal or vegetable, are con- 

 sidered to be transitory forms of the same organic type. 

 Kiitzing does not admit any essential distinction between 

 animals and vegetables. He maintains that the same 

 being may, at various periods of its development, assume 

 one nature or the other. The following is his theory in 

 a few words. Every organic being is constituted of 

 vegetable elements and animal elements, and according 

 as the one or the other prevails, the being becomes an 

 animal or a vegetable ; in the first stages of the develop- 

 ment of superior beings, and permanently in those of 

 inferior rank, the two elements are equally balanced. 

 And this is the case, in the author's opinion, with the 

 Diatomeae, which, on this account, cannot be absolutely 

 referred either to one series or the other, but constitute 

 the ring or circle which unites together all organic beings 

 into one kingdom. Long controversies have sprung up 

 between the supporters and the opponents of this doctrine, 

 who, to obtain victory, mutually accuse one another of 

 logical errors, of sophisms, and of paradoxes. 



The analysis of this controversy would be tedious and 

 of little profit ; whilst on the other hand, sound logical 

 principles may guide us to a rigorous estimate of the 

 facts. And, in truth, the natural sciences are entitled to 

 boast of a language that is adequate to the purpose, if 

 we avoid the abuse of Ontology. The words Animal and 

 Plant, like words in common use, as Species, Genus, Order, 

 Class, Kingdom, do not denote any existing thing in par- 

 ticular. To the naturalist there exist individuals only, 

 as to the philosopher there exist only bodies. Species is 

 a synthetical comprehensive expression, abstracted from 

 all the individuals so similar to each other, that they 

 may all be considered as originating from the same 

 parents. Genus is a still larger abstraction, comprehend- 

 ing all the species that resemble each other in some im- 

 portant characters ; and so we advance to the denomina- 

 tions animal and plant, expressions of ideas existing only 

 in the mind of man, and therefore entirely subordinate 



