Asks whether CD has any changes to make in a new German edition of Variation, which is to be published next year.

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].