Letter 8669
Haeckel, E. P. A. to Darwin, C. R.
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Thanks CD for Expression.
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Describes work on Die Kalkschwämme and its principal conclusions.
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The application of biogenetic law.
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Notes variability among calcareous sponges.
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Gastrula-like "Gastraea" as ancestor of multicellular animals.
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Posits homology between Hydra, Olynthus of calcareous sponges, and initial germ layers of higher animals.
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Comments on Lubbock's Prehistoric times [1865]
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and on David Strauss's Der alte und der neue Glaube [1872].