PROTOPLASMIC FUNCTION 47 



taking place around the periphery of the cytoplasm in a plane half-way 

 between the asters, and this constriction, deepening, finally cuts the 

 mother-cell completely into two parts, the new daughter-cells. The 

 chromatin masses, thickening, now gradually arrange themselves appar- 

 ently on the reticulum about the new attraction spheres, the rays disap- 

 pear, a nuclear membrane forms, the periphery of the cytoplasm rounds 

 itself, and the two new cells are become miniature replicas of their 

 mother-cell. 



HEREDITY AND ADAPTATION. Heredity and adaptation are two 

 opposed phases of the phylogenic or continued racial life of animals. 

 Heredity may be defined as that protoplasmic principle or faculty by 

 which cells tend to be like the parent-cells from which they spring. 

 Adaptation is the tendency of new protoplasm to adjust itself struc- 

 turally and functionally to the conditions of its environment. It is only 

 by the constant interaction of these two tendencies of all protoplasm 

 that life can continue unendingly. If only heredity determined the 

 characters of offspring, life would soon be overcome by an ever- 

 changing physical environment. 



On the other hand, were protoplasm too plastic, living forms would 

 lack that constancy of characteristics which marks each of them off 

 from the rest of the world. These two indispensable and interdependent 

 tendencies are, therefore, functions inherent in all protoplasm. Like 

 the other dispositions already considered, they are immediately dependent 

 (1) on the fluidity, (2) on the atomic or molecular complexity, and (3) 

 on the extreme instability of the living substance. These qualities of 

 protoplasm have already been described and explained. They are, in 

 fact, probably only different views or statements of the leading property 

 of biogen its extreme plasticity. By this property protoplasm is capable 

 of receiving on the one hand all the qualities of its parent protoplasm, 

 and on the other hand of accepting an impression from every surround- 

 ing influence, great or small. 



It is not difficult to imagine in regard to heredity that which has no 

 actual biological existence, and yet herein is apparently one of the great- 

 est mysteries of all of Nature's secrets. At the present time we cannot 

 well imagine how a body of jelly-like matter so minute as to be invisible 

 to the naked eye should be the sole means of transmitting from a man to 

 his son not only, sometimes, the whole physical constitution of that 

 man, but his mental and moral nature as well, habits of speech, tenden- 

 cies appearing perhaps scores of years after the heredity-conveying 

 speck of protoplasm from the parent is gone. The whole matter is 

 enormously complex and inwrought with speculation and skepticism. 



An Example of Relatively Simple Protoplasm: Ameba. Perhaps the 

 best way to give the reader an idea of the appearance and functions of 

 relatively undifferentiated or primal protoplasm is to describe one of 

 the more simple animals, in fact, the most simple animal known; unless 

 we suppose with Hackel that there lives an animal still more simple 

 in that it lacks a nucleus namely, the monera. 



