PEEFACE. XIX 



in tlie "General Morphology," and in the "History of 

 Creation," is wanting in actual proofs. The proofs are 

 there. Of course those who turn their eyes away from 

 them will not see them. Precisely that "exact" form of 

 analytical proof which the opponents of the descent theory 

 demand is to be found, by anybody who wishes to find it, 

 in the " Monograph of the Calcareous Sponges." 



Eknst Heinrich Haeckel. 



Jena, June 2Wh, 1873. 



