to the body, the anterior margin extending to the lower jaw. While floating on its back for several hours, during its helpless condition, it passes safely over the heads of its enemies, and is protected from being wrecked in sand or weeds. While in this almost motionless condition, it occasionally indulges in spasmodic efforts similar to those noticeable in freeing itself from the shell. After a few hours, becoming more vigorous, it gets to a depth of an inch or more below the surface of the water. After a day or two, the food-sac is less prominent and the fish experiences less difficulty in swimming at various depths. The young mackerel, hatched by Mr. Earll, were so hardy that forty were confined in a goblet without change of water for two days before the first fish died; others placed in water which was allowed to cool gradually, and immediately transferred to water ten degrees warmer, were not injured in the least. In fresh water they slowly sank and died in a few hours. Mr. Earll also found that a fair percentage of eggs could be hatched in still water with but one or two changes during their development. Eggs taken at 6 P. M. and allowed to remain in a basin of water till morning, when another change was made, hatched with very small percentage of loss. Samples of all the different stages of development were preserved in alcohol and glycerine for the National Museum. Over half a million were hatched by the various methods and at various times. 9. APPARATUS. The apparatus used in these experiments being made on the spot, though very primitive, was as successful as could possibly be desired. The apparatus consisted simply of floating-boxes with bottoms made of wire-cloth. The cloth was plated with nickel to prevent injurious action of the salt water and contained thirty-two wires to the inch. After it was found that a lot of fish had escaped through it, only the shells remaining to prove that hatching had taken place, the wire and each aperture were covered with coarse cotton cloth. The boxes were provided with covers for protection against storms, or wind or rain, but were provided with openings on the sides to admit fresh water from above. The box giving best results was arranged on a principle similar to that employed by Captain H. C. Chester in the experiments with codfish 8. FERTILIZATION. The eggs are easily fertilized. It is merely necessary that they come into contact with the milt of the male in any receptacle of water. A half hour after contact with the milt, the eggs swell and become too hard to be broken by the pressure of the thumb and finger. The water in which fertilization took place can then be replaced by clean water, and the eggs are ready for the hatching apparatus. Their specific gravity is now so nearly equal to that of salt water that when the water is at rest they float upon its surface, remain suspended in the water, or occasionally sink slowly to the bottom. The least current will cause them to be distributed through the liquid. Mr. Earll discovered a small oil globule in each egg which serves the purpose of buoying it. The impregnated egg is also so transparent that the fishermen, who are not usually very observing, would never suspect their presence. The eggs are smaller than eggs of almost any other species, and have an average diameter of only one-twenty-eighth of an inch. It has been estimated as will be seen that 21,952 would make a cubic inch, and a quart, 57 cubic inches, would hold 1,267,728 eggs. The period of hatching is greatly influenced by the temperature of the water. The average temperature during the experiments at Crisfield was 84 degrees Fahrenheit. Ten hours after contact with the milt the outline of the fish could be discerned by the naked eye. The fish is formed with the curve of its back at the lowest point of the egg. In fifteen and one-half hours, the fish began to hatch. In eighteen hours, one-half of the eggs had hatched, and in twenty hours, all were out. Experiments in water at 78 degrees Fahrenheit showed that 24 hours were necessary for hatching. A more remarkable effect of temperature is observed in the case of the cod. In water at 45 degrees, cod have been hatched in thirteen days; but in water at 31 degrees, fifty days were occupied in hatching. The newly hatched mackerel are about one-eighth of an inch in length, and so small as to escape through wire-cloth with thirty-two threads to the inch, and are almost colorless. The food-sac, situated well forward, is quite large in proportion to the body, the anterior margin extending to the lower jaw. While floating on its back for several hours, during its helpless condition, it passes safely over the heads of its enemies, and is protected from being wrecked in sand or weeds. While in this almost motionless condition, it occasionally indulges in spasmodic efforts similar to those noticeable in freeing itself from the shell. After a few hours, becoming more vigorous, it gets to a depth of an inch or more below the surface of the water. After a day or two, the food-sac is less prominent and the fish experiences less difficulty in swimming at various depths. The young mackerel, hatched by Mr. Earll, were so hardy that forty were confined in a goblet without change of water for two days before the first fish died; others placed in water which was allowed to cool gradually, and immediately transferred to water ten degrees warmer, were not injured in the least. In fresh water they slowly sank and died in a few hours. Mr. Earll also found that a fair percentage of eggs could be hatched in still water with but one or two changes during their development. Eggs taken at 6 P. M. and allowed to remain in a basin of water till morning, when another change was made, hatched with very small percentage of loss. Samples of all the different stages of development were preserved in alcohol and glycerine for the National Museum. Over half a million were hatched by the various methods and at various times. 9. APPARATUS. The apparatus used in these experiments being made on the spot, though very primitive, was as successful as could possibly be desired. The apparatus consisted simply of floating-boxes with bottoms made of wire-cloth. The cloth was plated with nickel to prevent injurious action of the salt water and contained thirty-two wires to the inch. After it was found that a lot of fish had escaped through it, only the shells remaining to prove that hatching had taken place, the wire and each aperture were covered with coarse cotton cloth. The boxes were provided with covers for protection against storms, or wind or rain, but were provided with openings on the sides to admit fresh water from above. The box giving best results was arranged on a principle similar to that employed by Captain H. C. Chester in the experiments with codfish at Gloucester, in the winter of 1878. It had openings on two sides even with the water line. Just below these on the outside of the box were wooden floats about three inches wide. These were placed at an angle with the surface so that the ordinary wave-action would cause the water to run up the slight incline, and after reaching the highest points, passed down through the wire-cloth into the box, thus giving a constant change of water without the aid of tide or currents. Other boxes were arranged in the ordinary way, to utilize the action of both tides and currents. These set obliquely in the water, so that the motion would force it through the bottom. In addition each had a large opening covered with wire-cloth below the surface of the water on its front side to give additional circulation. The boxes were moored in the harbor where the tide was strongest, and by means of them a greater part of the eggs was successfully hatched. The loss in one instance was less than fifteen per cent. 10. CONFIRMATION AND PRACTICAL RESULTS. After the experiments of Mr. Earll were over, very gratifying confirmation of the results reached by him was had in the microscopic studies of Mr. John A. Ryder, of the Fish Commission. The fish-hatching steamer "Lookout," under the direction of Major Ferguson, going down the bay, Mr. Ryder improved the opportunity to hatch a small number of fish and to make drawings of the embryo in different stages of development. He found that when the embryo was freed from the shell, the changes occurred rapidly. In seven hours he detected the outline of a fish; in seventeen, the head and eyes, and in twenty a free fish. He discovered the oil-globule attached to the lower end of the umbilical sac, which he pronounced to exist in no other fish which has been artificially propagated. At four days from the time of hatching, the globule having been absorbed, he observed the fish swimming vigorously about with open mouth, as if in search of microscopic food, and actually discovered traces of food in the stomach. Major Ferguson, the assistant commissioner, was so much pleased with the series of discoveries by Mr. Earll, and the confirmatory observations of Mr. Ryder, that he transported some of the young to Saint-Jerome Creek to watch their subsequent growth. Professor Baird has traced the stages of the investigation with the greatest interest and has furnished every possible facility. He will probably enter upon systematic hatching of the mackerel next summer with a view to stocking other waters. It is hoped that at least Narragansett bay may be reached as a northerly limit. The artificial propagation is entirely feasible and the season being in mid-summer would not conflict with the shad season of the spring, the salmon season of the fall, or the cod season of the winter. The eggs are much more abundant, and hatch more easily, as well as more speedily, than any other fish now propagated. During the four days consumed in hatching a lot of shad, five lots of mackerel could be hatched, and during twenty-four days necessary to hatch one lot of codfish, thirty-two lots of mackerel could be produced. Mr. Earll selected a suitable locality for a hatching station at Cherrystone, Md., on the eastern shore, preferring this to Mobjack bay at which the pounds are most numerous, on account of an excellent harbor. The fishermen are also very kindly disposed, and offered to render every assistance. Thus most important facts are added to the natural history of the fish and the prospect is bright for a great commercial success. ANTHRAX OF FRUIT TREES; OR THE SO-CALLED FIRE BLIGHT OF PEAR, AND TWIG BLIGHT OF APPLE, TREES. By T. J. BURRILL, of Urbana, Ill. THE widespread and disastrous disease of the pear tree, commonly called Fire Blight and that no less prevalent, at least in the western states, usually known as Twig Blight of the apple tree, are due to the same immediate agency. They are identical in origin and as similar in their pathological characteristics as are the trees themselves, or differ no more than one familiar with the histological structure of the trees might indicate, prior to observation upon the course and consequence of the malady. The quince and probably many other plants, among which we now name the butternut, the Lombardy poplar and the American aspen, suffer from the same disease. Judging from published descriptions only, |