The Visible Basis of Heredity 67 



to the young, nor is there any nerve connection 

 between the two. It is no wonder, then, that 

 the prying eye of the microscope has been turned 

 upon these reproductive cells, the eggs and 

 sperm, to see if there can be discovered in them 

 anything that may be regarded as the carriers 

 of the hereditary characters. Certain structures 

 have been discovered which many scientists 

 beUeve do constitute a visible physical basis of 

 heredity. 



The term "cell" applied to the egg is rather 

 unfortunate, for it calls up a vision of an empty 

 space surrounded by walls. The cells that 

 make up the animal and plant are, on the 

 contrary, masses of protoplasm, each usually 

 bounded by a layer of substance, the cell wall, 

 that is formed by the protoplasm; within each 

 cell is a small dense mass of protoplasmic 

 material, the nucleus, that is quite essential. 



Protoplasm is a somewhat jelly-like mate- 

 rial, almost transparent, sensitive, contractile, 

 capable of taking in and using certain food 

 substances to build new protoplasm. The 

 term is a collective term, somewhat as "society " 



