CAUSE OF HEREDITY 279 



cell, is a person who "lays one stone here, another brick 

 there, with reference to future development." How does 

 a skilled architect proceed to lay the foundations for his 

 structures? He would also do the same thing. He would 

 lay one stone here, another there, having in view and in 

 mind all the time what kind of a structure it is going to 

 be when it is finished. It is just as necessary for the cell 

 in building the skeleton on which the rest of the body will 

 be supported that he place and arrange the material and 

 particles of lime just so and all in the right place, keeping 

 in view what he intends to ultimately accomplish, as it is 

 for the skilled architect in building a house or a machine. 

 The cell must build the skeleton from lime, phosphorous, 

 etc., the ingredients must be mixed in proper proportions 

 and placed in the right place. So must man mix the mate- 

 rials of concrete and stone and place them in the right 

 place. The builder must have a mind that knows what is 

 necessary and required at every step. The following by 

 Mr. Wilson will illustrate how the cell in building animals 

 or plants must have the material with which to build or 

 else it cannot produce another individual like the one from 

 which it came. He says : 



"Every little organism at every stage of its existence 

 reacts to its environment by physiological and morpho- 

 logical changes. The developing embryo like the adult is 

 a moving equilibrium a product of the response of the 

 inherited organization to the external stimuli working 

 upon it. If the stimuli be altered, development is altered. 

 This is beautifully shown by the experiments of Herbst 

 and others on the development of sea urchins. Pouchet 

 and Chabry showed that if the embryos of these animals 

 be made to develop in sea water containing no lime salt, 

 the larvae fails to develop not only its calcareous skele- 

 ton but also its ciliated arms and a larvae thus results 



