WHAT IS AN ORGANISM? 175 



sessed of special cell-walls, but the lack of them may be due 

 to the imperfection of our vision, or to imperfectly formed 

 cells ; althouijh the cells whose existence appears intrinsically 

 dependent upon their own activity possess the nucleus, it 

 is not fully evident what the function is which the nucleus 

 plays. It is sufficient for the present purpose to note that it 

 is a specialization, by the activity of the whole cell, of a part 

 of itself for the execution of some function essential to the 

 existence of the cell as a whole. Morphologically it is a dif- 

 ferentiation of form and structure ; physiologically it is a 

 specialization, a division of labor or function, within the cell. 

 When the cell acts in generation the same principle is at work ; 

 that is, a partition of material substance, or of morphological 

 characters, with a retention of common interests. So long as 

 the segmentation of the yolk goes on there is the differentia- 

 tion of parts, but each part is essentially a part of the whole, 

 and the segmentation is but an increasing of parts with the 

 growth of the individual. As the segmented parts arrange 

 themselves into orderly series, and, like soldiers dividing into 

 platoons and companies, they march off to construct them- 

 selves into organs and tissues, the same principle of organic 

 growth is expressing itself in the organism — the enlargement 

 of the function of the whole by the increase of the number of 

 active parts. 



Differentiation and Specialization the Marks of an Organism. 

 — Differentiation and specialization are intrinsic marks of an 

 organism. They are essentially processes of increment of parts 

 and functions by division, and not by addition. The activity of 

 the organism ever tcndfe to increase heterogeneity, or dissimi- 

 larity of kind of its parts. The activity of non-organism 

 tends to the decrease of heterogeneity. In gravitation this is 

 illustrated wherever the law of gravitation expresses itself in 

 action ; two things tend to approach more nearly to a state of 

 uniformity regarding the law of gravitation, and so the final 

 end of activity of the law of gravity would be a perfectly 

 homogeneous mass, in which the attraction in every direction 

 would be uniform. So chemical action is a process by which 

 the heterogeneity of chemical composition is reduced ; the acid 

 and the salt unite to form a more stable compound, each of 



