REPRODUCTION 65 



would be open to so many accidents and 

 fraught with such difficulties as to be well-nigh 

 impossible. And yet, with every well-born 

 child that comes into the world, this is accom- 

 plished. But a human being is vastly more 

 than a successfully adjusted complex of cells 

 whose activities are sufficiently intricate and 

 adaptable to meet with success the ever-chang- 

 ing conditions around it. A human being is 

 a vast sum of conscious past experience, a 

 longing, desiring creature that seeks to mold 

 the future, a dreamer in hours of wakef ulness, 

 a thing of affections and feelings. And this 

 side of man's nature, too, is reproduced. 

 But by what process ? As in former cases we 

 shall attack this problem from its material 

 side. What are the physical conditions under 

 which reproduction is accomplished ? 



William Harvey, the discoverer of the cir- 

 culation of the blood, in his treatise on gen- 

 eration published in 1651, maintained that 

 " even on the same grounds, and in the same 

 manner and order in which a chick is engen- 

 dered and developed from an egg, is the em- 

 bryo of viviparous animals engendered from 

 a preexisting conception." This " preexisting 

 conception" was in Harvey's mind the exact 



