178 Causes and Course of Organic Evolution 



ganic bodies, continuity in form, in size, in molecular consti- 

 tution, in response to environal stimuli, will persist through 

 successive new formations or generations, so long as the rela- 

 tion of the organic or inorganic body to its environment, or 

 to environal agents that have gradually become intrinsic fac- 

 tors, remains the same. The growth by accretion of any crys- 

 tal, as compared with the growth by intussusception of any 

 inorganic or organic colloid body, represents the physical 

 difference of crystalloid and colloid aggregations. Heredity, 

 or like molecular structural continuity, is equally exhibited 

 however in both. But it still remains a moot point with physi- 

 cists as with physiologists whether colloids may not also grow 

 by accretion to their molecules. 



This hereditary principle explains why crystals of fluorspar, 

 formed during the silurian period in some drusy cavity of a 

 rock mass, exactly resemble others formed under like sur- 

 roundings during the eocene period, and why when exposed 

 in our day to subaerial environal agencies, side by side, both 

 will undergo analytic change. And it equally explains why 

 fossil examples of Lingula from the liassic formation exactly 

 resemble those of the present day, and also why, when such 

 are placed in a keenly competitive or in an unfavorable physi- 

 cal environment, they show analytic change and death. That 

 the fluor crystal is a solid crystalloid body, while Lingula 

 is a mixture mainly of labile colloid substances, is renewed 

 proof of Graham's contention — since often demonstrated and 

 extended — that matter may assume a crystalloid or a colloid 

 state under certain environal conditions. 



We can only regard disturbance of heredity then, or variation 

 as we generally designate it, to be due to changed environal 

 conditions, that act as stimuli to start responses or motions 

 of energized particles. The admirable illustrations of this, 

 marshaled and explained by Cope (73: 398-430) mainly from 

 the palseontological side of animal life, are a few of many like 

 illustrations which the studies of the past tliirty years have 

 brought together. 



Numerous definitions of heredity have been given, but most 

 of these apply mainly or only to man. H. Spencer well says: 



