Thanks for "Embryology of the fossil cephalopods", [Bull. Mus. Comp. Zool. Harvard 3 (1872–4): 59–112].

Regrets error in attributing acceleration concept to E. D. Cope instead of to AH in last edition of Origin, and misrepresentation of their joint view.

If decapod does not pass through zoea stage, is this acceleration? If hypothetical adult retained zoea characters, would this be retardation? Believes obliteration of growth stages frequently due to natural selection. Most interesting points in AH’s letter deal with senile characters. CD attributes them to laws of growth not selection. Explains degraded characters as result of readaptation to simpler conditions. Believes no innate tendency to progressive development exists.

Hopes AH visits F. Hilgendorf’s famous deposit [at Steinheim]. A. Weismann [Einfluss der Isolierung (1872)] makes good use of Hilgendorf’s observations.

Sends copy of last edition of Origin.

Respecting AH’s theory that acceleration of growth produces new characters, urges AH to examine decapods that do and do not pass through zoea stage. Believes there are no marked differences between them.