196 TRANSACTIONS OF THE 
Casper Wolff was not so easily convinced, and by 1759 
he was able to demonstrate that the chick was not pre- 
formed in the egg; that its parts were added in the course 
of development. This work was verified by other embry- 
ologists and the theory of preformation seemed forever 
knocked into a cocked hat. 
But not so. Yet it required more than a century to 
revive. In this time the cell had been discovered and its 
importance realized in part. A closer study of the cell re- 
vealed a nucleus and the nucleus chromosomes. Direct 
observation and experiments have shown these chromosomes 
to play an important role in heredity. 
Weismann made these the basis for his theory and on 
paper he formulated a most intricate super structure which 
he insisted must exist in a mature form in the chromosomes. 
His biophores and determinants, ids and idants were all 
there in the egg ready to direct the development of the in- 
dividual from the fertilized egg to maturity. But these 
ids, idants, chromosomes, etc. are contributions from similar 
structures in the parents; those chromosomes of the parents 
from those of the grandparents, and so on ad infinitum. It is 
true Weismann never advocated that a chick lay preformed 
in the egg, yet his theory certainly smacks strongly of 
preformation. 
And now the most recent experimental evidence is in 
a measure supporting Weismann’s theory. T. H. Morgan 
and his students are at work mapping out the characters in 
the chromosomes, or more accurately the factors for 
characters. A glimpse at the chart will make this clear. 
