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fresh water. I do not pretend to say that a fresh-water salmon never by any chance takes a particle of food, but that its doing so is so rare as merely to prove by its exception the generality of the rule. It must also be remembered that some fish will occasionally take a tempting bait more for sport than for food. A pike, when absolutely gorged with food, will not unfrequently seize a bait in his mouth, and yet refuse to swallow it, as trollers who use a gorge-bait well know. What does an artificial salmon-fly resemble in nature? Certainly no kind of winged insect, not even a gaudy libellula or agrion either in form or motion, for no libellula ever swims in the water, least of all after the fashion in which the artificial fly is made to locomote by the angler. Some have thought, among whom is Sir Humphrey Davy, “ that the rising of salmon and sea-trout at these bright flies, as soon as they come from the sea into rivers might depend upon a sort of imperfect memory of their early smolt habits.” But it is more probable the salmon takes the glittering fly—which is allowed to sink a little in the water—for a fish, for fish forms his principal food when an inhabitant of the sea. But be this as it may, the undoubted fact that the stomachs and intestines of fresh-water salmon are almost invariably found empty is a convincing proof, for reasons adduced above, that this fish abstains from food during its sojourn in fresh water.
4. With respect to the physiological paradox as to how an animal can live without taking food, it must be bome in mind in the first place, that, notwithstanding the voracity of the carnivorous fishes, and their extraordinary digestive capabilities, they are able to exist for long periods of time without food. Gold and silver fish may be kept for months without perceptible food, and certainly as we descend the scale of creation we shall find instances of long-continued abstinence more frequently. Snaiis in conchological cabinets have been known to live for years without a particle of food or drink. Frogs and toads will unquestionably exist for years immured in wood and stone in positions which entirely forbid the introduction of any kind of food.
But there must be a limit to this power of existing without food. A salmon, if he was never to eat, would undoubtedly die. But how, it will be asked, can muscular force be maintained for so many months without food? There can be no other explanation than this, that the salmon lives on his own abundant fat, stores of which are laid up throughout the whole body of the fish, but especially in the abdominal regions. This supply of fat was deposited during the time the salmon was an inhabitant of the sea, and when, as I have said above, he is a voracious feeder. Now we know, notwithstanding the assertion of old Izaak Walton* to the contrary, that the longer a salmon continues in fresh water the more does his flesh deteriorate. Mr. Alexander Russel, a good authority on salmon, is quite right when he says that “salmon taken in or near the sea are the best for food.” Let any one compare the difference in the quality of the flesh between a sea-salmon and one that has long been a sojourner in fresh water. He will notice in the sea-salmon the abdomen to be soft and tremulous with abundance of fat, that of the river-fish firm and comparatively destitute of fat. And this continued abstinence from food is, no doubt, in some measure the reason of the fish's gradual deterioration till the exhausting process of spawning renders the salmon now altogether unfit for food. The salmon's abode, therefore, in fresh water should be regarded as a quasi-hybernation, during which life is maintained upon stores already laid up in the organism. That muscular force may be maintained, and in fact that it is chiefly kept up by the combustion, not of the nitrogenous elements, but of the carbonaceous, has been rendered tolerably certain, and the circumstance that a salmon may move about for a long time in fresh water without supplies of food beyond his own abundant fat, is not actually much more than a further instanco of what takes place in hybernating animals, as the bear, which goes fat into winter quarters and comes out very thin. The same may be said with regard to experiments that have been made, showing that the Swiss mountains may be ascended solely upon the strength afforded by butter and other nonnitrogenous food.
According to the researches of Dr. John Davy, “the gastric juice, and probably the other fluids concerned in the function of digestion in fishes, are not secreted till the secroting organs are stimulated by the presence of food-a conclusion in harmony with a pretty general physiological law, and in accordance with what has been best ascertained respecting the gastric juice in other animals.” Dr. Davy infers the following corollary from the above, “that the migratory species of salmon, such as the salmon and sea-trout, which attain their growth, and become in high condition in the sea, there abundantly feeding and accumulating adipose matter, though not always abstaining in fresh water, which they enter chiefly for the purpose of breeding, are at least capable of long abstinence there without materially suffering.”+ He suggests the probability of this being owing to none of their secretions or
# Walton's words are:-“It is observed that the further they get from the sea, they be both fatter and better."
+ " Physiological Researches,” p. 168.
excretions, with the exception of the milt of the male and the roe of the female being of an exhausting kind.
The conclusion, then, at which I think we may safely arrive with regard to the food of the salmon is—that it feeds freely in the sea, and chiefly on other kinds of fish, such as sandlaunces, herrings, and other clupeide, though other animals, such as shrimps, and various crustacea occasionally form part of its diet ; that during its sojourn in the sea the salmon lays up a store of adipose matter; that it very seldom feeds during its abode in the fresh-water rivers, but lives on the supplies of its own internal fat; that though for some time the flesh does not perceptibly deteriorate, it is rendered poorer in quality towards the end of its sojourn in the fresh water, both from the exhaustion of its own supplies of fat and from the effects of spawning ; that it rapidly improves when it has reached the salt water, when it again lays up a fresh supply of adipose matter, which will support it during its sojourn in the rivers.
A SYNOPSIS OF THE RECENT BRITISH OSTRACODA.
BY GEORGE STEWARDSON BRADY, M.R.C.S., C.M.Z.S.,
(With Two Plate.) Of the various orders included in the great tribe Entomostraca, there is, perhaps, not one more generally interesting than that of which we propose to treat in the present paper. When we consider the great abundance and wide dispersion of the Ostracoda through the fresh waters and seas of our own period, and the countless myriads in which the shells of antediluvian species have come down to us, embedded in strata of varied character and age-for example, Silurian, Liassic, Carboniferous, Permian, Tertiary, and Post-tertiary-it will be evident that the geologist and palæontologist must, to a very large extent, share their interest in this group with the student of recent zoology and physiology. It will be seen also that any light which may be thrown upon the structure and habits of living forms must likewise be of great importance to the student of extinct species, as tending to exhibit more clearly their natural affinities, and to establish sounder principles of classification than can be attained by the study merely of the external covering of the animal, which only is left to us in the case of fossil examples. The prodigious numbers in which the fossilized carapaces of these creatures sometimes occur, is almost incomprehensible, some strata of certain rock formations seeming to be almost entirely composed of them. Amongst the recent species I know of no case analogous to this, except that of the dwellers in salt marshes and estuary mud; and I have no doubt that, were the mud-banks of our tidal rivers, and the swamps adjacent, suddenly petrified, we should, in many cases, find that the resulting stratified rock would exhibit as wonderful a concourse of once-living crustacean shells, as those which have just been spoken of. Mr. W. K. Parker has indeed conjectured, from a study of their fossil Rhizopoda, that the post-tertiary clays of the district round Peterborough constitute a littoral, brackish water-deposit; and it is remarkable that the Foraminifera there found, agree, to a very large extent, with those which I have myself taken in the salt marshes of our north-eastern coast. In strata much older than the post-tertiary, one would not, of course, expect to find species exactly identical with those now living. In washings of these clays, however, with which Mr. Parker has kindly supplied me, I have not been able to detect any shells of Ostracoda; it is, indeed, noticeable, that fossiliferous strata which are rich in Foraminifera are mostly poor in Ostracoda, and vice versa. Such, on consideration, one would naturally expect to be often the case. In all the salt marshes which I have had the opportunity of examining, living Ostracoda have been very abundant. If the net be passed carefully along the surface of the soft mud, so as to take up a thin layer, and the mass thus obtained be then washed through the net sufficiently to clear it of the fine ooze which will be found to constitute the greater part of its bulk, the residue will mostly consist of Ostracoda, living and dead, grains of sand, fragments of decaying vegetable matter, and very probably a good many living Foraminifera. This will mostly be the result wherever the water is brackish, and deposits a good deal of slimy mud, but in fresh water, or at the mouths of rivers, where the stream is clear and rapid, and does not produce much fine deposit, the Ostracoda, and other Microzoa, will be found much less plentifully. My belief is, therefore, that those strata which exhibit such very abundant and closelypacked remains of the smaller Cypridæ and Cytheridæ have most likely been formed in shallow, brackish lagoons, or at the mouths and deltas of rivers. The species of Ostracoda which I have found in these situations are, Cytheridea torosa (Jones), Cythere pellucida Baird, and Loxoconcha elliptica Brady; while in water, a little further from the saline influence, but still slightly partaking of it, it is not uncommon to meet with Cypris salina Brady, and Cypridopsis aculeata (Lilljeborg), as well as Entomostraca belonging to other orders. Some
along been very apportunity of"
und to Pulliciently thus ohtud, so
crustacea of larger type are also commonly met with in brackish waters,* e.g., Corophium longicorne, Palæmon varians, Mysis vulgaris, the common shrimp, etc.; but these, not having a hard, durable, calcareous investment, are not found in the fossil state. The Foraminifera which I have usually found in company with the Ostracoda above mentioned are, Polystomello striatopunctata, Quinqueloculina agglutinans, Trochammina inflata, Rotalia Beccarii, and Nonionina depressula ; the relative abundance of these forms varying with the locality.t The marshes of the Northumberland and Durham coasts are the only ones which have yet been carefully examined, and it is quite probable that other districts might yield different species.
By far the greater number of Ostracoda at present known have been described from fossil specimens, and the generic and specific characters have, of course, been taken almost exclusively from the external characters of the shell, the chief of these being, its general form and contour, mode of hingement, arrangement of lucid (or muscle) spots and style of surface ornament. The general structure of the animals themselves has indeed been known sufficiently to form good grounds of separation between some well-defined families, such as Cypridæ, Cytheridæ, and Cypridinidæ, but the more minute anatomy indicative of generic and specific differences has, until recently, been very little understood or investigated. The family Cytheridæ, for instance, has been considered by most authors as consisting of some three or four genera (or sub-genera of Cythere), separated from each other by shell-characters merely, and the family Cypridæ of two genera. But when we consider that, of the one hundred and thirty-scven species of Ostracoda now known as living in the waters of Great Britain, all except ten belong to these two families, and that amongst fossil species the disproportion is even greater, it is evident that, amongst so vast a number of species, many important differences of internal structure must exist, and that these stood in need only of careful investigation in order to form good grounds of generic subdivision. Accordingly, we find that much has of late years been done in this direction, more especially by Zenker and Fischer in Germany and Russia, and by Lilljeborg and G. O. Sars in Scandinavia. The researches
* See my paper on “Salt Marshes and their Inhabitants,” in INTELLECTUAL OBSERVER, Vol. v. p. 26.
+ Any readers of the INTELLECTUAL OBSERVER living in the neighbourhood of salt marshes or muddy estuaries would materially contribute to the knowledge of a very important and interesting branch of natural history by collecting the Microzoa in the manner above described. The best material for collecting.nets is “crinoline;" the things captured may be preserved, either by drying, or by immersion in dilute * spirit. I should myself be very glad of the opportunity of examining any such
collections, and would with pleasure name the specimens obtained.