ON THE 



ANIMAL NATURE OF DIATOMEA 



THE Diatomeae are microscopic beings provided with 

 a siliceous shield or shell, on which account their form 

 remains unchanged ; they are easily subjected to observa- 

 tion, and easily distinguished from other minute organ- 

 isms, whether belonging to the animal or the vegetable 

 kingdom. The earlier observers considered them to be 

 animals undoubtedly; and animals they were decidedly 

 pronounced by Ehrenberg. On the other hand, almost 

 every Algologist has actually taken them for plants, and 

 in this opinion all are agreed who have more recently 

 treated on the elementary structure of organic beings, 

 and on the distinctions that constantly separate animals 

 from plants, even at their first origin. In support of 

 their animal nature, the important observations of Ehren- 

 berg certainly possess great value, but these are in- 

 sufficient ; because the same arguments have induced the 

 illustrious author to include in the same class of Poly- 

 gastric Infusoria the Desmidieae also, which now by 

 universal consent are acknowledged to be true Algae. 



If a new opinion do not actually spring from between 

 these two, there is revived under another name the an- 

 cient theory of Phytozoa and Zoophytes, the Nemoures of 

 Gaillon, the Psychodiarian kingdom and the Arthrodieae 

 of Bory St. Vincent, the Green Matter of Priestley, the 

 metamorphoses of Agardh, and we are advancing directly 

 to the theory of spontaneous generation, and the other of 

 defective specific limitation, in accordance with which 



