TO A.WEISMANN.Down, May 1st, 1875.
I did not receive your essay for some days after your very kind letter, and I read german so slowly that I have only just finished it.

(268/1.
"Studien zur Descendenz-Theorie" I."Ueber den Saison-Dimorphismus," 1875.

The fact was previously known that two forms of the genus Vanessa which had been considered to be distinct species are only SEASONAL forms of the same species--one appearing in spring, the other in summer.

This remarkable relationship forms the subject of the essay.) Your work has interested me greatly, and your conclusions seem well established.

I have long felt much curiosity about season-dimorphism, but never could form any theory on the subject.