of a form embodying the most general propositions that can be affirmed
respecting the Cephalous Mollusca, standing in the same relation to them as
the diagram to a geometrical theorem, and like it, at once, imaginary and
true.") (in your sense, for I detest the word as used by Owen, Agassiz &
Co.) of each great class, I cannot doubt, is one of the very highest ends
of Natural History; and certainly most interesting to the worker-out.
Several of your remarks have interested me: I am, however, surprised at
what you say versus "anamorphism" (33/4. The passage referred to is at
page 63: "If, however, all Cephalous Mollusks...be only modifications by
excess or defect of the parts of a definite archetype, then, I think, it
follows as a necessary consequence, that no anamorphism takes place in this
group. There is no progression from a lower to a higher type, but merely a
more or less complete evolution of one type." Huxley seems to use the term
anamorphism in a sense differing from that of some writers. Thus in
Jourdan's "Dictionnaire des Termes Usites dans les Sciences Naturelles,"
1834, it is defined as the production of an atypical form either by arrest
or excess of development.), I should have thought that the archetype in
imagination was always in some degree embryonic, and therefore capable [of]
and generally undergoing further development.

Is it not an extraordinary fact, the great difference in position of the
heart in different species of Cleodora? (33/5. A genus of Pteropods.) I
am a believer that when any part, usually constant, differs considerably in
different allied species that it will be found in some degree variable
within the limits of the same species. Thus, I should expect that if great
numbers of specimens of some of the species of Cleodora had been examined
with this object in view, the position of the heart in some of the species
would have been found variable. Can you aid me with any analogous facts?

I am very much pleased to hear that you have not given up the idea of