Imágenes de páginas

The skates and dog-fishes are not the only marine animals that make curious ego-cases.

We have here three species of univalve shells, called by the Floridians, Conchs * (Busycont), which also make egg-cases. Each case is round and flat, about one-half to three-fourths of an inch in diameter, and one-sixth of an inch in thickness; the edge of each flat case is coarsely ribbed or milled, and numbers of them are strung together, only they are immovable upon the string, which is situated upon one side or edge, instead of being central as in a bead necklace. These egy-chains are sometimes two feet in length, and the cases are frequently bored into by different species of carnivorous mollusks to obtain the contents for food. These Conch animals were probably eaten by the aborigines, as we find the shells quite numerous in their Kjøkkenmeddings; they are now sometimes eaten by both the whites and negroes of Florida, but from appearances they must be tough chewing, and as indigestible as a rubber boot.

At the edge of the beach, rolling in the surf-ripples, a large fleet of Ark shells is coming ashore; these prettily ribbed bivalves look like the Cockles (Cardium), but the animal and the hinge are quite different. The velvety epidermis which generally covers the surface has been worn off by the friction of sand and water in the surf, exposing the clean white fabric of the shells; lighted by the sun they look like a squadron of little dismasted hulls. Two of the three species that we have here obtained are widely distributed, and may be picked up near Galveston, on the Gulf of Mexico. Some of the family may be found in every sea, and many species are used for food. The animal of Arca grandis, which is found in the Bay of Panama, is eaten by the natives; a single valve of this giant Ark

[ocr errors]

* Indiscriminately used when reference is made to any species of the Pyrulidæ, Strombidæ, Fasciolarida, etc., found here.

B. canaliculatum and B. carica of Linnæus, also collected by me as far north as New Bedford, and B. gibbosum of Conrad, the latter considered by many as only & variety of carica, but showing well marked peculiarities.

sometimes weighs two and a quarter pounds. Odd valves of the Ark shells are found in the shellheaps, but are not common.

A mile and a half from where the road enters the beach are the remains of two wrecks; the planking of the decks and sides has long ago been broken up and swept away by the sea, and the timbers projecting from the sands resemble the ribs of some gigantic mammal. No vestige of name is left; their wooden skeletons tell of fierce storms, when wind and waves, acting in unison, hurled ships and shells, and sea-weeds, like weightless bubbles, upon the beach. A wreck is a sad sight, but the crevices of an old hulk are a fine field for the naturalist, for many forms of marine life have a home therein. Here we found a tiny species of Mussel (Mytilus cubitus), and a new species of Siphonaria, a univalve shell shaped like a small shield, with elevated lines or ribs radiating from centre to circumference.

Without farther enumerating or explaining the prizes that are ours through the bounty of old ocean, we must retrace our steps towards the road, for the sun has so nearly set that its level rays are shining in our eyes. With baskets and pockets packed and full we jog along, stopping occasionally to pick up a fine specimen of a white bivalve shell, Dosinia discus, which is very abundant, thanks to a storm which threw them high and dry above the reach of ordinary tides. The Fish-crows (Corvus ossifragus) and a large species of Blackbird (Quiscalus baritus) are running over the wet sands, stooping sometimes to pick up some tit-bit for their suppers. Bidding them good-bye, we hurry on, and after a weary walk of what seemed many miles, made longer by the toilsome tug through sand and chapparal, we reach our haven; tired as dogs (at times are said to be) we gladly cast aside our packs, and after a refreshing wash, rush to supper with appetites as keen as hungry wolves

The evenings here are chilly, and a fire of the Pitch-pine wood (Pinus palustris Linn.) is pleasant, aside from the

[ocr errors]

warmth, for its bright flames fill the room with a cheerful light.

How glorious is sleep after a day of toil; of toil, yet still of pleasure. How gently it descends upon us, how quietly we yield to its embrace; it touches the drowsy eye, and we feel that

“The day is done, and the darkness

Falls from the wing of night."




The egg of a fish consists of an enveloping membrane containing the yolk or vitellus. The first step in the development of the egg is the formation of innumerable cells on the surface of the vitellus, which are closely packed together, and form a new membrane or layer surrounding the vitellus. The next sign of organization is the thickening and condensation of one spot of this new layer. The thickened part has an elongated oval shape, and in its centre, running longitudinally, is a delicate line or furrow.

This is the first beginning of the fish. The backbone of the fish is formed around this furrow. The anterior extremity spreads to become the cavity of the brain, and the tail grows from the posterior end. The yolk remains enclosed in the new layer as in a sac; as the fish grows this sac becomes constricted, so that the upper part of it is taken up into the body of the fish, while the lower part remains hanging out, and is called the umbilical vesicle, and it is in this condition that the fish is hatched. He is attached to the upper part of the umbilical vesicle, which being too heavy for him to move, he remains anchored by it, as it were, at the bottom of the stream, wriggling only his head and tail. The fish is fed by the absorption of the contents of the vesi

Fig. 47.

Fig. 48.

cle which decreases every day as he grows larger. After some days he is large enough to swim about with the vesicle under him, and at the end of forty to fifty days the sac is no longer to be seen, and the tish swims freely about.

All fish, however, are not perfect and oftentimes deformed ones are met with. Sometimes, instead of there being one fish only attached to an umbilical vesicle, there are two; not two separate ones, but two heads attached to one body, or two bodies attached to one tail, as shown in Figs. 47 and 48. This curious partial duplication of the fish takes place in the egg long before it is hatched, and is due, probably, to a bifurcation of the furrow around which the backbone of the fish is formed. The cells of the thickened oval spot, instead of forming one straight furrow, for some reason or other form one in the shape of a Y. Two backbones form around the two branches, with two heads, while one tail has to do for both.

As far as has been observed it is always the anterior part which is duplicated. No one body with two tails has been found. The tail remains single while the head and body are doubled ; and this duplication varies from a partial division of the head only to two nearly complete fish, with different brains, and hearts, and stomachs, and whose hearts do not even beat together, though the circulation in the tail must be common to both. On the other hand the head alone may show signs of duplication. One young fish was found in whom this had extended only to the partial division of the head. Of the four eyes the two middle ones were not completely separated; they looked something like a figure of 8 on its side. Generally one of the half fish is larger and stronger than the other, as seen in Fig. 48, and carries the smaller one off wherever it will, notwithstanding the apparent effort of the smaller one to go somewhere else.



These double fish are not very common, and as they die after the vitelline sac has been absorbed they are not seen by fishermen. The ratio of these deformed fish to the number of eggs in the hatching troughs was roughly estimated at twenty to twenty thousand, or one in a thousand eggs.

But a curious fact proved that the eggs of some fish contained a larger proportion. One large blind trout had a small pond to herself, and was fed daily by food presented to her on the end of a stick. Her eggs were kept apart, and out of about two thousand there were sixteen deformed fish, or one to one hundred and twenty-five eggs. Certain fish

would seem to be more predisposed to produce eggs creating these monstrosities, and were we to ask for the cause of this, we should probably have to look for it in some anomaly of the ovary of the fish which produces the eggs.

A deformity more common than the double fish is an apparent curvature of the spine. The fish instead of being straight, with the umbilical vesicle under him, is curved Fig. 49.

round so that its tail turns under, and sometimes touches the under surface of the sac he is attached to. Fig. 49 represents one of these semicircular fish. They are obliged

to swim on their side, and move round and round in a circle, or in a spiral, without being able to go straight.

These deformities are mentioned and treated by Buckland in his “Fish Hatching.” He there suggests that humpbacked deformity may have been caused by pressure during their "transport in the egg state.” In the instances mentioned above, however, there was no transport, the ova being taken from the fish on the spot.

Out of two thousand salmon ova hatched at Messrs. Dexter & Co's fish-farm, there were no deformities, but in another lot of about the same number there were two double-headed specimens just hatched out.

[ocr errors]
[ocr errors]
« AnteriorContinuar »