# Littell's Living Age/Volume 139/Issue 1792/Decorative Coloring In Freshwater Fleas

From Nature.
DECORATIVE COLORING IN FRESHWATER FLEAS.
There is something essentially comic in the notion of a freshwater flea — a species of the entomostracous crustaceous Daphnoidae — becoming beautifully ornamented with patches of scarlet and blue, for the purpose of seducing the affections of the opposite sex. If a scarlet coat is appreciated by the females of the very fleas of this great family to which we all belong, we ought not to be surprised at hereditary predispositions in favor of this color, and should conclude on this ground, as on many others, that the civilian male Anthropini of western Europe have taken a foolish and unnatural step, within the last hundred years, in abandoning the use of brilliantly colored clothing, and giving over the exceptional advantages which it confers to soldiers and huntsmen. The figures given by Prof. August Weismann, in the Zeitschr. wiss. Zoologie (1878, Supplement 1), show us the water-fleas, Polyphemus and Latona, most gorgeously got up in blue and scarlet. Goethe, though he never saw them, foretold their appearance: —
Es war enimal ein König, der hatt' einen gross-en Floh, Den liebt' er gar nicht wenig, als wie seinen eignen Sohn,
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In Sammet und in Seide, war er nun ange-than, Hatte Bander auf den Kleide, hatt' auch ein Kreuz daran, etc., etc.
It is to the elaborate and ingenious studies of Prof. Weismann on caterpillars — worthy to be placed by the side of the most original of Mr. Darwin's own investigations — that we owe our knowledge of an exceedingly important cause of animal coloration, namely, that which is explained by the term "startling" or "terrifying" coloration (Schreckfarben). Just as in various human races the amorous of both sexes paint their face and adorn their bodies in order to attract one another, so nature paints by sexual selection, and just as we dress ourselves up in wigs and gowns and spectacles, or tattoo our countenances in order to terrify evil-doers so (Prof. Weismann shows) does nature paint masks with staring eyes upon the feeble caterpillar's back in order that he may enjoy the privileges so usually gained by the ass in the lion's skin. Brilliant patches of color occur only in a few Daphnoidæ (also in a few Phyllopoda), and after a very detailed investigation as to the variations which these patches of color present in the different species, in the two sexes, and at different seasons and at different periods of growth, Prof. Weismann comes to the conclusion that they must be regarded as a decoration acquired by sexual selection which probably was first of all confined to the male sex, but subsequently, in most cases, became transmitted also to the other sex. Probably a reciprocal and alternating sexual selection favored this transference to the female sex, the most brilliant females being chosen by the few males existing at the commencement of a sexual period, and the most brilliant males being chosen by the relatively few females existing at the end of such a period. The existence of these "sexual periods" is a well established feature in the life-history of entomostraca, alternating with parthenogenetic periods. From the fact that neighboring colonies of the same species have a constantly differing arrangement of color, it appears probable that the development of these decorative color-patches took place after the isolation of the colonies, that is to say, subsequently to the glacial period in northern Europe. The transference of the decorative coloration originally developed only by the males, took place in three directions — firstly to the other sex; secondly to the not-yet sexually mature period of growth; and thirdly to the parthenogenetically produced generations. In the various species of Daphnoidæ with decorative coloration we find different degrees of completeness of the transference in these three different directions. Only one species, viz., Latona, presents the highest degree or complete transference of the coloration to both sexes, all stages of growth and all generations of the annual cycle. Prof. Weismann concludes that the Daphnoidæ afford a further case in favor of the hypothesis that secondary sexual characters can be converted into general characteristics of the species, and that they confirm Mr. Darwin's theory of the origin of the color-patterns of butterflies' wings.