200 SENESCENCE AND REJUVENESCENCE 



success. The crystal is fundamentally a physical individuation 

 among molecules of like chemical constitution, although in certain 

 cases some heterogeneity of composition occurs. In the organism, 

 as the facts show, individuation is evidently associated with 

 chemical activity, and widely different substances may enter into 

 the constitution of the individual. The mere existence of axes in 

 both the organism and the crystal, which is one of the grounds for 

 comparison, is no criterion of essential similarity, for axes may be 

 the expression of very different conditions in different cases. No 

 adequate evidence for the identity or similarity of the axes of the 

 organism and those of the crystal has ever been presented, and 

 there is much evidence to show that they are very widely 

 different. 



Apparently two distinct types of individuation exist in the 

 organic world. In the one, which may be called the centered or 

 radiate type, the parts are arranged and their behavior is integrated 

 with reference to a central region; in the other, which we may call 

 the axiate type, with reference to one or more axes. The radiate type 

 of individuation appears most clearly in the simple cell and in the 

 radiate structures which arise within it in connection with division, 

 while the axiate type is found both in cells and in organisms. More- 

 over, the two types of individuation often appear in combination: 

 in the starfish, for example, the body as a whole possesses an oral 

 aboral axis in the direction between the two surfaces, and the arms 

 are axiate structures with longitudinal and transverse axes, but 

 they are arranged radially about a central region. Most unicellular 

 organisms and most cells which form parts of multicellular organ- 

 isms show indications of a more or less definite and permanent axis 

 or axes superimposed upon the centered activities of the cell. In 

 the organism, as contrasted with the cell, the axiate type of indi- 

 viduation is predominant, and the axiate organization becomes 

 increasingly definite, conspicuous, and permanent as individuation 

 advances. In fact, the very general occurrence of an axiation of 

 some sort, or of physiological polarity as it is commonly called, is 

 the foundation of the belief widely current among zoologists that 

 polarity is a fundamental characteristic of protoplasm. While 

 most cells undoubtedly do possess at least temporary polarity, 



