Feels sure that at times the globe must have been superficially cooler. Believes CD will turn out right with regard to migration across the equator via mountain chains, while the tropical heat of certain lowlands was retained.

Has returned memorial to Chancellor of Exchequer; thanks CL for his note.

Lengthy remarks on cool period. Did not know of CL’s interest. New facts in new German and English [4th] editions of Origin will be too late for CL’s use. CD’s ten-year-old MS on cool period is available.

Thanks RC for photograph and for papers, which are of highest interest to CD. He is not fully convinced about the rose by RC’s graft-hybrid paper [Bull. Congr. Int. Bot. & Hortic. Amsterdam (1865): 65–80]. Still retains faith in his own view that no plant is perpetually self-fertilised.

Surprised at Hooker’s introducing "so organic a change as a deviation in the axis of the planet" to explain the cold of the Glacial Period.

Thanks CD for German translation of Origin.

Droughts over the summers have brought about changes in the numbers of plants and animals in the area. The small quantity of Orchestia darwinii that has survived the changes no longer includes two previously common male forms. Great changes also take place without such unusual physical conditions. The disappearance of a briefly abundant bryozoan in local caves has made way not for the return of original bryozoan inhabitants but for a completely new fauna.

Gives details of enclosed MS on cool period. Mentions Hooker’s opposed "axis of the earth" view. Causes of glacial period are beyond CD; "cannot believe change in land and water being more than a subsidiary agent".

Reviewing C. V. Naudin’s article ["Nouvelles recherches sur l’hybridité dans les végétaux", Ann. Sci. Nat. (Bot.) 4th ser. 19 (1863): 180–203] for Popular Science Review [5 (1866): 304–13]. Requests references.

Proposes to visit Down on Easter weekend.

Comments on cool-period MS. Still believes geographical changes principal cause of former changes of climate.

Thanks for references for his Naudin–hybridism paper [see 5029].

On the "bullae" as constant, regular generic characters in Hymenoptera. Disagrees with Louis Jurine ["Observations sur les ailes des hyménoptères", Mem. Accad. Sci. Torino 24 (1820): 177–214].

Asks, on behalf of his father, whether he might publish a new German translation of the Origin, believing Bronn’s to be inadequate.

Forgot to thank CD for his praise of tendril paper [see 4944].

Cannot come to Down on weekend because of teaching duties.

Describes plans for new German edition of Origin [1867].

Thanks for the paper on Sterrha (McLachlan 1865).

Oswald Heer [in Die Urwelt der Schweiz (1866)] agrees with CD that Swiss ants (Formica sanguinea) capture more slaves than do British ants. Does this contradict selection, since the British ants are exposed to harder conditions and a poorer fauna?

Writes on slave-making ants; cannot explain why fewer slaves are caught in England than in Switzerland.

Sends CD comb of the Chinese honey-bee, as requested.

Asks [Secretary] to list the proper titles of foreign societies of which he is an honorary member; he has mislaid diplomas.

Calls for more study of behaviour and less of classification to determine whether descent theory can bear the weight not [only] of reasoning but of fact. Hopes CD’s intended book [Variation] will help.