Dear Darwin

Unless I am mistaken you have somewhere given the story of a dog which, on a breezy day, growled when he saw an opened umbrella moved by the wind. I want to make use of the instance, but cannot find it. Can you tell me where it is?¹

I yesterday referred to your work on the Cirrhipedia for the purpose of seeing whether you said anything about their sensitiveness to passing shadows. I find that you have noted it in respect of individuals in the water with their cirrhi expanded.² You do not say, however, that it is noticeable with those which are left exposed by the retreating tide, and which, having their valves but loosely closed, close them tightly when a shadow is cast on them. Have you ever observed this?³

Sincerely yours | Herbert Spencer