25* GENETICS 



2. PREFORMATION AND EPIGENESIS 



How does germplasm transmute into somatoplasm? 



Historically there have been two conspicuous at- 

 tempts to solve the riddle of differentiation, neither of 

 which gives intellectual satisfaction any longer in the 

 light of what is known to-day. 



The first held sway in the 17th and 18th centuries 

 under the guise of the preformation theory which as- 

 sumes that development is simply the unfolding and en- 

 larging of what was already present in the germ in 

 miniature. This has been called the theory of "emboite- 

 ment" or "infinite encasement,' 5 because, not only is 

 the miniature plant or animal supposed to be packed 

 within the germ-cell like the embryo plant between the 

 cotyledons of the bean seed, but within each miniature 

 also it is supposed that the next generation is encased, 

 and the next, ad mfinitum. Aided by a poor microscope 

 and a good imagination the theory of preformation 

 was carried to such an extreme that a mannikin or 

 "homunculus" was actually figured by Hartsoeker 

 seated within the head of a human spermatozoan ! 



The second attempt to solve the riddle of develop- 

 ment resulted in the theory of eplgenesis which goes 

 to the other extreme, maintaining that organization 

 gradually appears out of an absolutely simple undiifer- 

 entiated germ. This theory had its most influential ex- 

 position in "Theoria Generationis" by C. F. Wolff in 

 1759. "The mistake in the doctrine of preformation 

 was in supposing that germinal parts were of the same 

 kind as adult parts; the mistake of epigenesis was in 

 maintaining a lack of specific parts in the germ." 



