600 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



organisms are to each other in their structure and chemical constitution, the 

 more similar as a rule are also their individuality differentials, and that to 

 more fundamental differences in chemical constitution and structure corre- 

 spond furthergoing genetic differences in the organismal differentials. In 

 the course of phylogenetic evolution the finer organismal differentials devel- 

 oped gradually; at least they became manifest only in the course of advancing 

 evolution. Likewise, as evolution progressed, an increasing differentiation 

 and specialization of tissues and organs took place. Comparable processes occur 

 during embryonal development ; but here the organismal differentials develop 

 from precursor substances, the complexity of which increases parallel to the 

 increasing complexity of the organs and tissues and organismal differentials 

 in the higher organisms. 



However, during ontogenetic development endstages are reached in which 

 again a decline sets in in the manifestation of the more specific organismal 

 differentials. The more the cellular substance proper of organs and tissues 

 diminishes and the more the paraplastic and intercellular substances predomi- 

 nate, the more specific is the organ and tissue differentiation and the less 

 prominent become the finer organismal differentials, the species and individu- 

 ality differentials. The character of the lens of the eye, and presumably also 

 that of keratin and of other specialized structures which no longer possess the 

 typical cellular constitution of the tissues from which they originated exem- 

 plify this change. But this is found only if certain serological reactions are 

 used as tests for the presence of organismal and organ differentials ; by 

 means of contact and distant effects of transplanted tissues it is still possible 

 to demonstrate the presence of individuality differentials in such tissues, 

 at least in the case of the eye lens. It is therefore probable that in these 

 paraplastic tissues the individuality differentials have not been entirely lost, 

 but that their existence cannot be demonstrated by the less sensitive serological 

 methods ; this may be due to the fact that they have relatively diminished in 

 quantity perhaps on account of the increasing preponderance of the organ 

 differentials. 



Evolution is essentially the history of the adaptations between organisms 

 and their environment and between constituent parts within the organism, 

 the non-adapted organisms being eliminated. But there has been an evolution 

 not only in the development of the organisms, their tissues, organs, and their 

 organismal differentials ; there has been an evolution also in those processes 

 which lead to the decline of these organisms, such as ageing, tendency to dis- 

 ease, and death, all of which are manifestations of the lack of perfect adapta- 

 tion. Primitive organisms possess great plasticity in organ formation and 

 they possess the ability to restitute the whole organism under the influence 

 of internal and external environmental factors. This plasticity is associated 

 with a lack of the manifestation of finer organismal differentials and there- 

 fore with a lack of individuality. The higher organisms constitute much more 

 rigid, fixed wholes, which exhibit very fine individuality differentials. In the 

 higher organisms the organ systems have become more complex in structure 

 and function, and in their interaction with other organ systems. The primitive 



