THEORY OF EMBOITEMENT 7 



groups composing the bodies from which it was derived, 

 hence the offspring is like its parents and not like any other 

 kind of animal. Further, when once differentiation has 

 taken place, and the cells derived from the fertilised ovum 

 have formed the different tissues that go to make up the 

 body of the organism, the cells forming these tissues will, 

 under ordinary conditions, produce cells similar to them- 

 selves and not another kind of cell. The cells forming the 

 skin will, when they divide, produce skin cells, cells forming 

 the liver will produce liver cells, and so on. 1 We are thus 

 forced to the conclusion that cells produce similar cells or 

 groups of cells to the cells or groups of cells from which they 

 are derived. 



The knowledge that the fertilised ovum produces an 

 organism similar to the two organisms from which it is 

 derived, has given rise to several theories. 



The earliest fully formed theory that professed to explain 

 how it is that the fertilised ovum produces a complete 

 organism like the parents from which it is derived, was the 

 theory of emboitement. This theory was worked up in the I 

 greatest detail by Bonnet. It assumed that the egg con- ' 

 tained a fully formed animal in miniature. Every part of it 

 was there, although very small, all the parts being packed 

 very closely together. The development simply consisted in 

 the growth and unfolding of these already existing parts. 

 When this theory of emboitement Avas pushed to its logical 

 conclusion, even its upholders were bound to admit that in 

 the case of a hen, for instance, the egg contained not only 

 a miniature chicken, but that that miniature chicken must 

 contain all the miniature eggs for the next generation ; that 

 these miniature eggs must in turn contain still more minute 

 chickens, that these minute chickens again contain still more 

 minute eggs, which again contain chickens, and so on for all 

 generations down to infinity. It is only fair to say that 

 Bonnet himself eventually renounced this theory. 



Darwin's theory of pangenesis assumes that the germ /- 



1 See pp. 45, 68, 69. 



