Between England and the West Indies, about the time when one begins to recover from the first bout of sea-sickness, we come upon a certain sluggish tract of ocean, uninvaded by either Gulf Stream or arctic current, but slowly stagnating in a sort of endless eddy of its own, and known to sailors and books of physical geography as the Sargasso Sea.  The sargasso or floating seaweed from which it takes its poetical name is a pretty yellow rootless alga, swimming in vast quantities on the surface of the water, and covered with tiny bladder-like bodies which at first sight might easily be mistaken for amber berries.  If you drop a bucket over the ship’s side and pull up a tangled mass of this beautiful seaweed, it will seem at first to be all plant alike; but, when you come to examine its tangles closely, you will find that it simply swarms with tiny crabs, fishes, and shrimps, all coloured so precisely to shade that they look exactly like the sargasso itself.  Here the colour about is less uniform than in the arctic snows, but, so far as the sargasso-haunting animals are concerned, it comes pretty much to the same thing.  The floating mass of weed is their whole world, and they have had to accommodate themselves to its tawny hue under pain of death, immediate and violent.

Caterpillars and butterflies often show us a further step in advance in the direction of minute imitation of ordinary surroundings.  Dr. Weismann has published a very long and learned memoir, fraught with the best German erudition and prolixity, upon this highly interesting and obscure subject.  As English readers, however, not unnaturally object to trudging through a stout volume on the larva of the sphinx moth, conceived in the spirit of those patriarchal ages of Hilpa and Shalum, when man lived to nine hundred and ninety-nine years, and devoted a stray century or so without stint to the work of education, I shall not refer them to Dr. Weismann’s original treatise, as well translated and still further enlarged by Mr. Raphael Meldola, but will present them instead with a brief resume, boiled down and condensed into a patent royal elixir of learning.  Your caterpillar, then, runs many serious risks in early life from the annoying persistence of sundry evil-disposed birds, who insist at inconvenient times in picking him off the leaves of gooseberry bushes and other his chosen places of residence.  His infant mortality, indeed, is something simply appalling, and it is only by laying the eggs that produce him in enormous quantities that his fond mother the butterfly ever succeeds in rearing on an average two of her brood to replace the imago generation just departed.  Accordingly, the caterpillar has been forced by adverse circumstances to assume the most ridiculous and impossible disguises, appearing now in the shape of a leaf or stem, now as a bundle of dark-green pine needles, and now again as a bud or flower, all for the innocent purpose of concealing his whereabouts from the inquisitive gaze of the birds his enemies.