FROM MONER TO MAN. 583 



branches of a tree receive the life-supporting sap from a common 

 trunk, so all living forms have a common origin in protoplasm with 

 which the evolution of their life begins ; the entire growth and devel- 

 opment of the body consisting in the growth and differentiation of 

 the protoplasm of which its tissues and organs are composed. 



Observe how admirably the figure of a tree exhibits the supposed 

 relationship between the various types of animals both extinct and 

 living ; indicating, not that each tyjje has been derived directly from 

 one immediately preceding it, either in time or in structural rank, 

 but that various types have had a common ancestor from which, by 

 development in different directions, all have more or less diverged ; 

 so that the relationship between man and the existing anthropoid apes, 

 for example, is that of remote cousinship rather than of direct descent. 

 The common stock is represented by the trunk of the tree ; from this 

 trunk, which rises higher and higher with each diverging offshoot, has 

 sprung an immense variety of branches ; and, at the very pinnacle of 

 this magnificent structure, man appears — the crowning efflorescence 

 of organic evolution. 



The permanent types which represent these various phases of em- 

 bryonic development show a progressively increasing differentiation 

 from their environment. The moner and the amoeba are almost as 

 structureless as the water in which they are found, consisting of little 

 more than water with a trace of albumen ; in specific gravity, in tem- 

 perature, in color, etc., the difference between these low organisms and 

 their environment is slight. Compared with the differences — chemi- 

 cal, physical, and structural — between man and the invisible atmos- 

 phere in which he is submerged, the contrast in this particular is a 

 striking one. This leads us to other considerations of still greater sig- 

 nificance. 



The true environment of any organism consists in as much of the 

 external universe as that organism is capable of holding communica- 

 tion with ; so that, as the life becomes higher, the environment also 

 becomes more complex. 



At the deep-sea bottom, where life is exhibited in its most simple 

 grades, the temperature is unvarying ; no light penetrates to those 

 depths ; a uniformity of conditions is thus preserved almost unbroken, 

 and the adjustments necessary to the continuance of life under such 

 circumstances are as trifling as the grade of life is simple. 



By the greater complexity of the human organism as compared 

 with other animals, man is brought into communication with and 

 under the influence of a vastly increased variety of external condi- 

 tions, mainly through the organs of the special senses and their inti- 

 mate relations with a highly developed nervous system. 



That without the eye and its connections with the brain we could 

 have no consciousness of light is the merest commonplace of physiol- 

 ogy ; yet, could we realize the full meaning of this and other similar 



