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hasty investigation can possibly master its difficulties : many of the clefts are extremely minute, and the shadows, by which alone they can be detected, are in proportion fugitive, so as to require watching, literally, almost from hour to hour, in order to trace their continuation and connection. It would be well, too, to check our results in the opposite illumination, though the large clefts, at least, are not so distinct in the waning moon.
A little way out of our diagram to the N. lies the fine crater Manilius (24) 25 miles in diameter: the broad and peak- and crater-besprinkled ring of which attains in general a luminosity of 8°, and so becomes always a conspicuous object; it may be perceived even in the lunar night, and was one of Ħ's pseudo-volcanoes. The E. side attains 7700, the W. 7500f. (Schr. found 7500 E., 8000 to 9900 W., and the W. wall 2200f. above the plain).
Between Manilius and Menelaus (15), Schr. has represented very dark spot of an oval form, to which he gave the name Boscovich. L., though he represents it, seems not to have thought it worthy of a name, and has transferred the appellation, without notice (a most unusual procedure with him), to another dark spot half-way between it and Agrippa, where it has been recognized by B. and M., and is shown in our diagram. From Mr. Birt's observations it seems that B. and M. have failed in delineating this region (the old site); Schr. and L. seem to be nearer the present state of the surface, but the dark tone given by Schr. seems either to be visible only under certain circumstances, or to have subsequently faded. In these districts the flat ring-form so common elsewhere, is supplanted by openings, or intermissions among the parallel ridges universally prevalent here, so that two of their sides only are bordered by a rampart. Of this kind is Julius Caesar, a large steel-grey depression, of only 1° in reflective power at the N. end, becoming as bright as 3° southwards. In its peculiar aspect Chacornac traces the effect of a retreating tidal wave, which he thinks may have penetrated it from the neighbouring sea; and he considers this as one of the many evidences of similar action. Several dark valleys unite it with a similar, but much smaller and not quite so dark, formation at some distance N. On its W. side the true crater Sosigenes, 14m. broad, and, according to Schr., 3700f. deep, intervenes between it and the M. Tranquillitatis : at a little distance E. is the Boscovich of L., and B. and M., another very dark spot of the same kind.
JUPITER'S SATELLITES. As the planet Jupiter is now conspicuous, though not so high as desirable, the following particulars of his system will be interesting. Sept. 6th. I. in transit, 7h. 56m. to 10h. 16m., its shadow 8h. 14m. to 10h. 34m. II. ditto, 8h. 26m. to 11h. 18m., its shadow Oh. 2m. to 11h. 54m.—13th. I. in transit, 9h. 40m. to 12h., its shadow 10h. 9m. to 12h. 28m. II. ditto, 10h. 43m. to 13h. 35m., its shadow 11h. 39m. to 14h. 32m. (These two will be beautiful spectacles.) —20th. I. in transit, 11h. 25m. to 13h. 45m., its shadow eliers 12h. 4m. II. enters 13h. 2m.-22nd. I. leaves disc 8h. 11m., its shadow 8h. 52m.-29th. I. in transit, 7h. 38m. to 9h. 57m. its shadow 8h. 27m. to 10h. 47m.
OCCULTATIONS. Sept. 7th. B.A.C. 6292, 6 mag. 9h. 49m. to 10h. 22m.8th. p’ Sagittarii, 5. mag., 9h. 47m. to 10h. 51m.
THE FOOD OF THE SALMON.
BY W. HOUGHTON, M.A., F.L.S.
DIFFERENCE of opinion has long prevailed with regard to what constitutes the food of the salmon. As I have lately been examining a large number of the stomachs of this fish, it may interest the readers of this magazine to hear the conclusion at which I have arrived. But let us first of all see what authors have said on this question. The earliest mention of the food of the salmon with which I am acquainted, occurs in Gesner's work “De Aquatilibus," p. 828. Quoting Hector Boëthius, he says,
“On what food the salmon lives, or whether it lives on any at all, is as yet a doubtful question, since, when disembowelled, the stomach shows nothing but a certain thick fluid.” Gesner then adds, “I myself also, whenever I have examined a dissected specimen, have never found anything in the stomach and intestines except a yellowish mucus and particles of white grit.* Our fisherinen affirm that they never find anything in the stomachs of the large fish, but only in those of the smaller ones; for the larger ones which are known by the name of salmon, live on nothing but water, preferring that which is thick and muddy as being more nutritious. But I have heard from an old and experienced fisherman that the fish, until it is a true salmon, feeds on aquatic lice, but that after spawning it will eat any fish that happens to come in its way; the fisherman said he had frequently found fish in their insides.” Shaw says, “All fishermen agree that they never find any food in the stomach of this fish. Perhaps during the spawning time they may entirely neglect their food, as the Phocæ, called sealions and sea-bears, are known to do for months together during the breeding season, and it may be that like those animals, the salmon returns to sea lank and lean, and comes from it in good condition. It is evident that at times their food is both fish and worms, for the angler uses both with good success, as well as a large gaudy fly, which the fish probably mistakes for a gay libellula, or dragon fly” (“Gen. Zool.” v. Part I., p. 42). The preposterous idea that any fish can subsist without ever taking food was maintained by Daniel, who stoutly argued that the salmon lived on nothing but water ! Dr. Knox states that from the time the salmon enters the fresh water it ceases to feed, properly speaking, although it may occasionally rise to a fly, or be tempted to attack a worm or a minnow, in accordance seemingly with its original habits as a smolt. But after first descending to the ocean and tasting its marine food, it never again resorts to its infantilo food as a constant mode of nourishment. This great fact, he continues, well understood by fishermen and anglers, has been placed by Mr. Young, of İnvershaw, beyond all doubt. Nothing is ever found in the stomach and intestines of the fresh sea salmon but a little reddish substance, which Dr. Knox, after a careful microscopic examination, concluded to be the ova of some species of Echinodermata. Of the salmon, therefore, while in the sea, he maintains this to be the sole and constant food.
* “ Album lapillum.” I suspect he means by these words the masses of calcareous crystals so frequently found in the intestines of salmon.
M. Valenciennes describes the salmon as voracious, and states that its food consists of fishes (Ammodytes Tobianus), but Dr. Knox asserts that there exists not a single fact in the history of British salmon to support this opinion. He refers to various fanciful theories suggested by fishermen and others in regard to the marine food of the salmon, and concludes by stating that in spring, as the spawn fish are descending with the smolts, they may occasionally be tempted with an artificial fly or lob-worm, but as to their feeding regularly in rivers, Mr. Young's experiments have negatived the assumption beyond all doubt. Dr. Knox is here partly right and partly wrong;
he is right in saying that the fresh-water salmon seldom or ever feeds, but unquestionably wrong in maintaining so positively that other fish never constitute the salmon's food in the sea. The same writer thought that the excellent quality of the salmon as an article of food is to be traced to the rich eggs of the Echinodermata, which he considered to be its principal food.
Mr. Yarrell writes as follows_" That the salmon is a voracious feeder may be safely inferred from the degree of perfection in the arrangement of the teeth, and from its known habits, as well as from the well-known habits of the species most closely allied to it; yet of the many observers who have examined the stomach of the salmon to ascertain the exact nature of that food which must constitute their principal support, few have been able to satisfy themselves.”* Faber says that “the common salmon feeds on small fishes, and various small marine animals.” Dr. Fleming, as quoted by Yarrell, remarks that their favourite food in the sea is the sand eel, and Yarrell says he has himself taken the remains of sandlaunce from the stomach. That herrings enter largely into the list of the food of the salmon while in the sea, I can stato from personal observation. The salmon in whose stomachs I frequently found one, two, three, or even four herrings together, were from the coast of Norway. Some of the herrings were nine or ten inches long. I never found any other fish in their stomachs, nor, indeed, any other kind of food. This, however, will do no more than prove that salmon feed greedily enough on herrings, and not that other fish do not form part of their diet. There is an abundance of herrings off the coast of Norway, and probably they were more readily captured by the salmon than other fish, during the months of May, June, and July, at which time I made my examinations.
With respect to the river or fresh-water salmon, I never detected the smallest trace of food of any sort either in the stomach or intestines; and Mr. Bowring, a most respectable fishmonger at Wellington, obligingly examined for me a great number of stomachs. We neither of us ever found any food in them, nothing but a thick white or yellow mucus with the gritty particles already noticed, and some intestinal worms, amongst which tape-worms were the
mnost common. But it is asserted by many that the idea of a salmon abstaining from food the whole time the fish is an occupant of fresh water, is a physiological heresy; that so active a fish must eat in order to maintain itself and supply muscular force ; and that the very fact that salmon are taken with minnow, worm, or fly, is a convincing proof that they do feed in fresh water; that the vacuous condition of the stomach is readily accounted for by the well-known habit this fish has, in common with many others, of emptying its stomach when hooked or netted, by an instinctive act of fear, or to facilitate its escape by lightening its load. That the salmon does occasionally throw up the contents of its stomach is probable enough, and has indeed been witnessed. “I was
* See “ British Fishes,” ii. p. 52.
on the sea in a boat,” writes Mr. Campbell, “rowing, one bright, calm day, along some rocks near the mouth of a salmon river, when I espied one of the poaching nets used by the Highlanders. ... We went towards the net, and in so doing started a salmon, which dashed into it. I saw the salmon strike and entangle itself, and in a moment begin to vomit a number of herring-fry. I could see them quite distinctly, for we were exactly over the fish. I pulled up the net as fast as I could, and in a second the salmon was in the boat. So quick was I, that there were upwards of a dozen of the fry still in his mouth, although he had been ejecting a shower of them as I drew him to the surface. Of course there was nothing in his stomach; but the idea of saying that salmon do not eat is ridiculous. I have myself caught scores with a worm, and thousands are so taken every year, which sufficiently proves that they eat; but when they find themselves fast on a hook or in a net, they disgorge, like the Solan goose, or as the salmon did that I have just described, and thus nothing is found in their stomachs when they are opened.”*
Another way of accounting for the absence of food in the salmon's stomach is by its extraordinary digestive properties. “The rapid growth of the fish seems to imply that its digestion must be rapid, and may perhaps account for there never being food in its stomach when found.”+
Let us examine these various arguments.
1. The salmon vomits up his food when hooked or netted, consequently he has nothing in his stomach. Granted that he does sometimes, does it follow that he always does so ? Or if he always did so, can he vomit up the indigestible portions from the intestines ? For it must be remembered that the whole intestinal tract in river-salmon, as a rule, never shows evidence of food. But since herrings and other fish are frequently found in the stomachs of sea-salmon, it is evident that the vomiting theory must fall to the ground. If they invariably eject the food from their stomachs in fresh water, why do they not invariably do so in salt ?
2. The rapid digestion will account for the absence of food in the stomach. But if river-salmon feed, as asserted, there must be times at which the fish is caught immediately after having swallowed some food; for though the digestion may be rapid, it cannot be instantaneous. Besides, the digestion theory will not account for the absence of all indications of food in the intestine.
3. The fact that salmon are frequently taken with a worm, minnow, or fly, is a proof that the fish do feed whilst in the
* "Life in Normandy,” pp. 36 and 37. Ed. 1865. + " Harvest of the Sea," p. 192.