My dear Sir

Color

I am delighted to have a letter from you again & to see a part of it in your own hand writing:¹

In regard to color in Crustaceæ my personal experience is limitted to British specimens.² I know of none in which variation of color is dependent upon sex. Specimens vary sometimes but I have attributed the variation to other causes: Deep water specimens are generally redder than those which live near the shore: I have thought this to be dependent upon the less amount of light in deep water. Oceanic species that live near the surface of the water very frequently are of a deep Indigo blue: There is a species of Idotea that differs little or nothing from one of our littoral species except in being of an uniform deep Blue—where as the shore species differs from reddish brown to light green according to the colour of the weed on which it lives (feeding)— Brachyscelus lives on medusæ I believe & a great number of specimens should be examined before it could be determined that the variation in color is not due to other causes than that of sex.³

Gelasimus lives generally in holes on the sea shore. It is probably the case that the male is the more active and erratic of the two,⁴ thus light might influence the color of the more exposed sex:

I received recently a curious little species of crab from Borneo, that lives in a sponge: I could always tell the males from the females by the amount of epidermis rubbed off the dorsal surface of the females, being much more than from the males: The Females nestled closer & more constantly in the sponge than the males, which were necessarily more erratic & consequently less rubbed.⁵

You will thus perceive that I believe that whenever color varies in the sexes it is due to a change of habit only & would be the same in the female if the two were under like circumstances

I have however two rather large collections that I am now looking over, in which the collectors have attended much & noted the colors of the animals when alive & if I find any reason to modify this expression of my opinion I will write to you

Structure of Male

I do not know that the males fight for the females at least to any great extent: I remember once putting in two males of Carcinus mænas—our common shore crab—into a pan with a female. The female before having been put into the pan had been in the possession of a small male. But when I looked again she was in possession of the larger—that is the stronger animal— If they fought for possession the victory was a Bloodless one for I saw no wounds or injury.

Once I remember separating a male & female Gammarus from each other. they were in a pan with a great many others   The female swam immediately towards the mass of others that were congregated together   the male dashed fiercely round the pan two or three times & then in amongst the crowd of others & took the same female out from among the mass of others—but there was no fighting for possession of the female. it may have been as I think generally is the case with them that the females were the more numerous.⁶

The claws in this species are a trifle larger in the males than in the females but not more important that is sufficient to assist them in grasping the female well—one hand being thrust forward the other back thus hitched under the segments of the female.

The males have no other weapons for fighting than the females, except that in many the chelæ are developed larger— among our British species are the following genera in which the males have larger chelæ than the females⁷

Stenorhynchus Achaeus

Inachus

Eurynome.

Cancer.

Ebalia

Corystes.

Porcellana

Galathea andrewsii⁸

amphipoda

Orchestia

Allorchistes

Gammarella

Melita

Podocerus

Erichthoneus⁹

Dulichia

Caprella

Exotic. are

Gelasimus¹⁰

Gegarcinus¹¹

Parthenope

There are others I dare say but I do not at present recollect them, but I believe that often species are made of the two sexes because of the different size limbs

Believe me My dear Sir | yours very sincerely | C Spence Bate.