Thanks CD for Expression.

Describes work on Die Kalkschwämme and its principal conclusions.

The application of biogenetic law.

Notes variability among calcareous sponges.

Gastrula-like "Gastraea" as ancestor of multicellular animals.

Posits homology between Hydra, Olynthus of calcareous sponges, and initial germ layers of higher animals.

Comments on Lubbock’s Prehistoric times [1865]

and on David Strauss’s Der alte und der neue Glaube [1872].