Extreme cases of terrestrial animals, once aquatic in habits, throw a flood of lurid light (as the newspapers say) upon the reason why this should be so. For example, frogs and toads develop from tadpoles, which in all essentials are true gill-breathing fish. It is, therefore, obvious that they cannot lay their eggs on dry land, where the tadpoles would be unable to find anything to breathe; so that even the driest and most tree-haunting toads must needs repair to the water once a year to deposit their spawn in its native surroundings. Once more, crabs pass their earlier larval stages as free-swimming crustaceans, somewhat shrimp-like in appearance, and as agile as fleas: it is only by gradual metamorphosis that they acquire their legs and claws and heavy pedestrian habits. Now there are certain kinds of crab, like the West Indian land-crabs (those dainty morsels whose image every epicure who has visited the Antilles still enshrines with regret in a warm corner of his heart), which have taken in adult life to walking bodily on shore, and visiting the summits of the highest mountains, like the fish of Deucalion's deluge in Horace. But once a year, as the land-crabs bask in the sun on St. Catherine's Peak or the Fern Walk, a strange instinctive longing comes over them automatically to return for a while to their native element; and, obedient to that inner monitor of their race, down they march in thousands, velut agmine facto, to lay their eggs at their leisure in Port Royal harbour. On the way, the negroes catch them, all full of rich coral, waiting to be spawned; and Chloe or Dinah, serves them up hot, with breadcrumbs, in their own red shells, neatly nestling between the folds of a nice white napkin. The rest run away, and deposit their eggs in the sea, where the young hatch out, and pass their larval stage once more as free and active little swimming crustaceans.
Well, crabs, I need hardly explain in this age of enlightenment, are not fish; but their actions help to throw a side-light on the migratory instinct in salmon, eels, and so many other true fish which have changed with time their aboriginal habits. The salmon himself, for instance, is by descent a trout, and in the parr stage he is even now almost indistinguishable from many kinds of river-trout that never migrate seaward at all. But at some remote period, the ancestors of the true salmon took to going down to the great deep in search of food, and being large and active fish, found much more to eat in the salt water than ever they had discovered in their native streams. So they settled permanently in their new home, as far as their own lives went at least; though they found the tender young could not stand the brine that did no harm to the tougher constitutions of the elders. No doubt the change was made gradually, a bit at a time, through the brackish water, the species getting further and further seaward down bays and estuaries with successive generations, but always returning to spawn in its native river, as all well-behaved salmon do to the present moment. At last, the habit hardened into an organic instinct, and nowadays the young salmon hatch out like their fathers as parr in fresh water, then go to the sea in the grilse stage and grow enormously, and finally return as full-grown salmon to spawn and breed in their particular birthplace.
Exactly the opposite fate has happened to the eels. The salmonoids as a family are freshwater fish, and by far the greater number of kinds—trout, char, whitefish, grayling, pollan, vendace, gwyniad, and so forth—are inhabitants of lakes, steams, ponds, and rivers, only a very small number having taken permanently or temporarily to a marine residence. But the eels, as a family, are a saltwater group, most of their allies, like the congers and murænas, being exclusively confined to the sea, and only a very small number of aberrant types having ever taken to invading inland waters. If the life-history of the salmon, however, has given rise to as much controversy as the Mar peerage, the life-history of the eel is a complete mystery. To begin with, nobody has ever so much as distinguished between male and female eels; except microscopically, eels have never been seen in the act of spawning, nor observed anywhere with mature eggs. The ova themselves are wholly unknown: the mode of their production is a dead secret. All we know is this: that eels never reproduce in fresh water; that a certain number of adults descend the rivers to the sea, irregularly, during the winter months; and that some of these must presumably spawn with the utmost circumspection in brackish water or in the deep sea, for in the course of the summer myriads of young eels, commonly called grigs, and proverbial for their merriment, ascend the rivers in enormous bodies, and enter every smaller or larger tributary.
If we know little about the paternity and maternity of eels, we know a great deal about their childhood and youth, or, to speak more eelishly, their grigginess and elverhood. The young grigs, when they do make their appearance, leave us in no doubt at all about their presence or their reality. They wriggle up weirs, walls, and floodgates; they force there way bodily through chinks and apertures; they find out every drain, pipe, or conduit in a given plane rectilinear figure; and when all other spots have been fully occupied, they take to dry land, like veritable snakes, and cut straight across country for the nearest lake, pond, or ornamental waters.
These swarms or migrations are known to farmers as eel-fairs; but the word ought more properly to be written eel-fares, as the eels then fare or travel up the streams to their permanent quarters. A great many eels, however, never migrate seaward at all, and never seem to attain to years of sexual maturity. They merely bury themselves under stones in winter, and live and die as celibates in their inland retreats. So very terrestrial do they become, indeed, that eels have been taken with rats or field-mice undigested in their stomachs.
The sturgeon is another more or less migratory fish, originally (like the salmon) of freshwater habits, but now partially marine, which ascends its parent stream for spawning during the summer season. Incredible quantities are caught for caviare in the great Russian rivers. At one point on the Volga, a hundred thousand people collect in spring for the fishery, and work by relays, day and night continuously, as long as the sturgeons are going up stream. On some of the tributaries, when fishing is intermitted for a single day, the sturgeons have been known to completely fill a river 360 feet wide, so that the backs of the uppermost fish were pushed out of the water. (I take this statement, not from the 'Arabian Nights,' as the scoffer might imagine, but from that most respectable authority, Professor Seeley.) Still, in spite of the enormous quantity killed, there is no danger of any falling off in the supply for the future, for every fish lays from two to three million eggs, each of which, as caviare eaters well know, is quite big enough to be distinctly seen with the naked eye in the finished product. The best caviare is simply bottled exactly as found, with the addition merely of a little salt. No man of taste can pretend to like the nasty sun-dried sort, in which the individual eggs are reduced to a kind of black pulp, and pressed hard with the feet into doubtful barrels.
In conclusion, let me add one word of warning as to certain popular errors about the young fry of sundry well-known species. Nothing is more common than to hear it asserted that sprats are only immature herring. This is a complete mistake. Believe it not. Sprats are a very distinct species of the herring genus, and they never grow much bigger than when they appear, brochés, at table. The largest adult sprat measures only six inches, while full-grown herring may attain as much as fifteen. Moreover, herring have teeth on the palate, always wanting in sprats, by which means the species may be readily distinguished at all ages. When in doubt, therefore, do not play trumps, but examine the palate. On the other hand, whitebait, long supposed to be a distinct species, has now been proved by Dr. Günther, the greatest of ichthyologists, to consist chiefly of the fry or young of herring. To complete our discomfiture, the same eminent authority has also shown that the pilchard and the sardine, which we thought so unlike, are one and the same fish, called by different names according as he is caught off the Cornish coast or in Breton, Portuguese, or Mediterranean waters. Such aliases are by no means uncommon among his class. To say the plain truth, fish are the most variable and ill-defined of animals; they differ so much in different habitats, so many hybrids occur between them, and varieties merge so readily by imperceptible stages into one another, that only an expert can decide in doubtful cases—and every expert carefully reverses the last man's opinion. Let us at least be thankful that whitebait by any other name would eat as nice; that science has not a single whisper to breathe against their connection with lemon; and that whether they are really the young of Clupea harengus or not, the supply at Billingsgate shows no symptom of falling short of the demand.
AN ENGLISH SHIRE.
For the reasons which have determined the existence of Sussex as a county of England, and which have given it the exact boundaries that it now possesses, we must go back to the remote geological history of the secondary ages. Its limits and its very existence as a separate shire were predetermined for it by the shape and consistence of the mud or sand which gathered at the bottom of the great Wealden lake, or filled up the hollows of the old inland cretaceous sea. Paradoxical as it sounds to say so, the Celtic kingdom of the Regni, the South Saxon principality of Ælle the Bretwalda, the modern English county of Sussex, have all had their destinies moulded by the geological conformation of the rock upon which they repose. Where human annals see only the handicraft and interaction of human beings—Euskarian and Aryan, Celt and Roman, Englishman and Norman—a closer scrutiny of history may perhaps see the working of still deeper elements—chalk and clay, volcanic upheaval and glacial denudation, barren upland and forest-clad plain. The value and importance of these underlying facts in the comprehension of history has, I believe, been very generally overlooked; and I propose accordingly here to take the single county of Sussex in detail, in order to show that when the geological and geographical factors of the problem are given, all the rest follows as a matter of course. By such detailed treatment alone can one hope to establish the truth of the general principle that human history is at bottom a result of geographical conditions, acting upon the fundamentally identical constitution of man.