On THH’s paper on cephalous Mollusca [Philos. Trans. R. Soc. Lond. 143 (1853) pt 1: 29–66]. Discovery of the type or "idea" (in THH’s sense, not Owen’s or Agassiz’s) is one of the highest ends of natural history.
Discusses anamorphism;
position of heart in Cleodora.
Variability within species;
cementing process in cirripedes.