CHAPTER 12.. 1843-1846: Age 36-39.

1843-1846: AGE 36-39.

Completion of Fossil Fishes.--Followed by Fossil Fishes of the Old Red Sandstone.--Review of the Later Work.--Identification of Fishes by the Skull.--Renewed Correspondence with Prince Canino about Journey to the United States.--Change of Plan owing to the Interest of the King of Prussia in the Expedition.--Correspondence between Professor Sedgwick and Agassiz on Development Theory.--Final Scientific Work in Neuchatel and Paris.--Publication of "Systeme Glaciaire."--Short Stay in England.--Farewell Letter from Humboldt. --Sails for United States.