164 GEOLOGICAL BIOLOGY. 



are in intimate association in the organism, and the instant 

 the organism ceases those changes incident to growth there re- 

 mains the inert residt of the Hving, that is, the dead, animal. 



Living Implies Change, and Change is Incessant in a Living 

 Organism. — Living impHes change in the organism, and inces- 

 sant change. This change is what makes growth possible. 

 The organism at any particular stage is only the morphologi- 

 cal result of the previous growth, and what we recognize as 

 the adult form of the individual is as truly mutable as the 

 species itself. The individual organism, if exactly defined, 

 is not precisely the same for any two days or moments of its 

 existence, but one of its fundamental characteristics is that 

 it grows, i.e., it has development. Almost the same might 

 be said of any of the parts or organs : so long as they are 

 acting they are undergoing waste, and repair, and incessant 

 change; as soon as this process ceases they cease their 

 organic function, decay, and return to their material ele- 

 ments. In the organ, in the individual, in the species, or 

 in the whole organic kingdom, the morphological form and 

 the physiological function are of a temporary nature, and 

 thus essentially differ from the physical or chemical proper- 

 ties of matter. 



An Organism is an Aggregate of Cells. — An analysis of a 

 plant or animal demonstrates it to be composed of " cells." 

 Each individual organism is morphologically an aggregate of 

 cells ; these cells are not all alike, nor are they combined in 

 the same manner. Another proposition may be accepted 

 without further examination : every animal or plant begins its 

 " existence as a simple cell, fundamentally identical with the 

 less modified cells which are found in the tissues of the adult." 



The Organic Cell the Morphological Unit.- — The simplest form 

 of the cell, or, as Huxley calls it, a " morphological unit," 

 may be conceived of as a mere mass of protoplasm devoid of 

 cell-wall and nucleus. He sets forth as fundamental proposi- 

 tions that, I. '' For the whole living world the morphologi- 

 cal unit, the primary and fundamental form of life, is merely 

 an individual mass of protoplasm, in which no further struc- 

 ture is discernible; 2. That independent living forms may 

 present but little advance on this structure; and 3. That all 



