332 



significance, in both Zoology, and Physiology, is at once quite 

 prominent, for familiar as we now are with the general relations 

 of the Cell — the fundamental unity of living bodies — it is an 

 inquiry not a little important what combination of organic parti- 

 cles is necessary to characterize a real individual animal. 

 Kolliker (" Ueber die Gattung Gregarina," in the Zeitsch. f. 

 Wissensch. Zool. I., p. 10, 1848), has described as a distinct 

 animal, a simple, nucleated cell, a closed sac with neither mouth 

 nor arms, and which, he says, lives an independent existence. 

 Now, it is true that the beginning of all individual animal life is 

 from the same elementary body — a simple, nucleated cell ; it is 

 equally true that those combinations of particles which, on this 

 basis, lead to the formation of all animals, consist only in the 

 multiplication and aggregation of this same cell body, so that, 

 everywhere, the fertilized ovum is only a repetitional compound 

 of its first simple element. These facts indicate a beautiful 

 unity and simplicity attending the first appearance of all living 

 forms ; but, suggestive as they are, I do not think that they war- 

 rant, in the present state of science, the view that simple, 

 unmodified nucleated cells may be each, under any circum- 

 stances, a distinct, individual animal. They may, indeed, be 

 the transitional, immature forms of real animals, exactly as the 

 ovum of a Medusa is a round bunch of cells, swimming freely 

 about, in a very animal-like manner, by means of cilia ; we 

 cannot regard this ovum, at that time, as the true animal, al- 

 though it is the potential one in future ; neither, in the same 

 way, may we look upon the ciliated, moving, cell-like bodies, 

 which constantly fall under the eye of the microscopist, as any 

 thing but the germs or immature parts of higher forms. 



The correctness of this view will be the more apparent if we 

 consider, for a moment, the existing state of the subject of Infu- 

 soria. The organized forms, included under this class, embrace 

 the most heterogeneous elements of both the vegetable and ani- 

 mal kingdoms ; and difficult as it is to pursue, step by step, the 

 history of those invisible forms from their origin to their death, 

 it must be a long time before we shall have any thing like a 

 satisfactory knowledge of their real character. Many of the 

 late studies seem, if any thing, to have rendered the subject 

 more perplexing than ever, for they have declared that some of 

 the so-called Infusoria, hitherto regarded as among the most 



