The great importance of the Gastraea theory lay in the fact that it linked up, by means of the biogenetic law, the germ-layer theory with the doctrine of evolution. It supplied an evolutionary interpretation of the earliest and most important of embryogenetic events, the process of layer-formation. Upon the Gastraea theory or its implications were founded most of the phylogenetic speculations which subsequently appeared. Upon the Gastraea theory Haeckel based a system of phylogenetic classification which was intended to replace Cuvier's and von Baer's doctrine of Types. This took the form of a monophyletic ancestral tree. Its main outlines are given on p. 290 in graphic form, combined and modified from the table on p. 53 of the 1874 paper and the genealogical tree given in the _Kalkschwaemme_.[434] _Monophyletic Genealogical Tree of the Animal Kingdom, based upon the Gastraea Theory and the Homology of the Germ Layers_. _______________________________________________________________________ | | | . | | | | m | | | _Vertebrata_. | o | | . | | | l | | m | _Arthropoda_. | | e | | r | | | | o | | e | | | | c | | d |_Echinoderma_. | | _Mollusca_. | | | d | | | | | | a | | n | | | Sagitta. \______ | ______/ | | | | e | | | | \|/ | . d | | | | | | | | a n | | y | | | | Nematoda. Himatega. | i a | | b | | | | | | | r | | | | | | | | | a d | | | | | | | | | t o | | | \______________|______|_ __|____________|_____/ | a o | | | \/ | m l | | | | ae b | | | _Coelomati_ | H | | | (worms with body-cavity}. | | h | | | \ / | t | | | \ / | i | | | \ / | W | | |________________________________\/_____________________|______| | . | | | | | ) d | | | . |