184 UNIVERSITY OF MISSOURI BULLETIN 



there, or is the development the coming into existence of one 

 thing after another from a beginning which is "without form 

 and void," so far as any^ essential resemblance to the adult 

 organism is concerned? The preformationists of the eight- 

 eenth century went so far as to develop their elaborate theory 

 of encasement, by which the germ was supposed to contain 

 all of the adult structures in miniature, including the germs 

 of all future generations, enclosed one after another in ever 

 decreasing magnitude, like toy eggs within eggs carried in- 

 ward to infinity. Of course it did not take a very extensive 

 examination of embryonic stages to discover that the general 

 course of development in all embryos was by epigenesis and 

 not by evolution, that the egg had at first no resemblance 

 to the future adult and attained its adult state by epigenesis 

 or the gradual moulding and modification by insensible degrees 

 of its constituent parts. But, nevertheless, the question between 

 epigenesis and preformation has in a modified form engaged 

 the attention of experimental embryologists during recent 

 years. 



The eggs of certain animals, among others the frog, sea- 

 urchin and starfish, are fertilized and develop without parental 

 care in the open water. Here experiments are possible which 

 could hardly be made upon an egg developing in a brood- 

 pouch or other internal cavity of the parent. The question as 

 to whether the protoplasm of an egg is in any sense organized 

 or preformed, in the sense that certain parts of it are destined 

 to give rise to certain parts of the adult, has been attacked 

 by the actual removal of parts from even minute eggs, and, if 

 the egg survived the operation, a comparison made of the 

 resulting embryo with one of normal development. Thus, 

 pieces have been cut from fertilized and from unfertilized 

 eggs ; two, four, eight and even sixteen cell stages have been 

 shaken apart and, in this latter case, the constituent cells in 

 some instances have been found capable of development into 

 normal individuals of fractional size. So many and so diverse 



