102 Trans. Acad. Set. of St. Louis. 



Weismann has postulated for the germ-plasm a complicated 

 architectural structure which is a definite and predetermined 

 arrangement of elementary vital units, each of which is des- 

 tined to form a particular and definite part of the body. 

 These units are distributed during the course of cell-divisions 

 occurring in embryological development to their respective 

 positions in the body where they control and determine the 

 development of those special structures only which they are 

 destined to form. And, furthermore, he maintains that a 

 certain undifferentiated portion of the germ-plasm is passed 

 into the germ-cells where in the next generation it becomes 

 in turn disintegrated in forming the body of the offspring. 

 He thus postulates an uninterrupted continuity for the germ- 

 plasm which bridges across the gap from one generation to 

 the next, as contrasted with the perishable body of the organ- 

 ism which is destroyed at the death of each individual. 



Much of Weismann' s doctrine has been recently shown to 

 be without a foundation of fact, and great as has been its 

 influence in stimulating the progress of this phase of zoologi- 

 cal investigation, the theory has been largely given up for an 

 epigenetic view of organic development. 



According to epigenesis the organism is not preformed in 

 the germ in all its final complexity of structure, but many of 

 the characters of the adult arise secondarily during develop- 

 ment, being the result of the interaction of internal and 

 external forces and coming into existence only after many 

 cells have been formed by division and grouped in different 

 ways both in relation to each other and to their environment. 



As to the ultimate problem of heredity and development, 

 zoology is still completely in ignorance. Weismannism throws 

 it one step farther back and transfers it from the visible to 

 the invisible, without supplying a real explanation. Epigene- 

 sis has no answer at all, not even a formal one, to the funda- 

 mental questions of heredity and development. What we 

 want to know is this : What is the peculiar organization of 

 the germ- plasm upon which we are driven to believe inheri- 

 tance depends, and what is the power that controls the intri- 

 cate phenomena of development and directs them to a definite 

 and foreseen end? In* some way the nature of the individual 



