THE OYSTER-INDUSTRY. 211 



lu front of tlie giUs, that is, between tliem and the hinge, there are four fleshy flaps— the lips— two on each side of the body. They 

 are much like the gills in appoaianec, and they are connected with each other by two ridges which run across the middle of the body '. 

 close to the anterior end, an<l between these folds is the large oval nxouth, which is thus seen to bo situated, not at the open end of thd 

 shell but as far awav from it as possible. As the oyster is immovably fixed upon the bottom, and has no arms or other structures for 

 seizinn- food and carrying it to the mouth, the question how it obtains its food at ouco suggests itself. If a fragment of one of the gills 

 is examined with a microscope, it will be found to be covered with very small hairs, or cUia, arranged in rows. Each of these cilia is 

 constantly swinging back and forth, with a motion something like that of an oar in rowing. The motion is quick and strong in one 

 direction and slower in the other. As all the cilia of a row swing together, they act like a line of oars, only they are fastened to the gill, 

 and as this is immovable, they do not move forward through the water, but produce a current of water in iXw opposite direction. This 

 action is not directed by the animal, for it can be observed for hours in a fragment cut out of the jjiH, and if such a fragment be supplied 

 with fresh sea-water, the motion will continue until it begins to decay. While the oyster lies undisturbed on the bottom, with its muscle 

 relaxed and its shell open, the sea-water is drawn on to the gills by the action of the cilia, for although each cilium is too small to be seen 

 without a microscope, they cover the gills in such great numbers that their united action produces quite a vigorous stream of water, 

 which is drawn through the shell and is then forced through very small openings on the surfaces of the gills into the water-tubes, inside 

 the gills, and through these tubes into the mantle cavity, and so out of the shell again. As the stream of water passes through the gills 

 the blood is aerated by contact with it. The food of the oyster consists entirely of minute animal and vegetable organisms and small 

 particles of organized matter. Ordinary sea-water contains an abundance of this sort of food, which is drawn into the gills with the 

 water, but as the water strains through the pores into the water-tubes, the food-particles are caught on the surface of the gills by a layer 

 of adhesive slime which covers all the soft parts of the body. As soon as they are entangled the cilia strike against them in such a way 

 as to roll or slide them along the gills toward the month. When they reach the anterior ends of the gills they are pushed off and fall 

 between the lips, and these again are covered with cilia, which carry the particles forward until they slide into the mouth, which is 

 always wide open and ciliated, so as to draw the food through the oesophagus info the stomach. Whenever the shell is open these cilia 

 are in action, and as long as the oyster is breathing, a cm-rent of food is sliding into its mouth. 



The cilia and p&rticles of food are too small to be seen without a microscope, but if finely powdered carmine be sprinkled over the gills 

 of a fresh oyster, which has been carefully opened and placed in a shallow dish of sea-water, careful observation will show that as .soon as 

 the colored particles touch the gills they begin to slide along with a motion which is quite uniform, but not nuich faster than that of tho 

 minute-hand of a watch. 



This slow, steady, gliding motion, without any visible cause, is a very striking sight, and with a little caro tho particles may be 

 followed up to and into the mouth. 



In order to trace the course of the digestive organs, the visceral mass may be split with a sharp knife or razor. If the split is 

 pretty near the middle of the body, each half will show sections of the .short, folded cesophagus, running upward from the mouth, and 

 the irregular stomach, with thick semi-transparent walls, surrounded by the compact, dark-greenish liver. Back of the liver and stomach 

 the convoluted intestine will be seen, cut irregularly at several points by the section. 



The coils of the intestine arc imbedded in a light-colored mass of tissue— the reproductive organ — which forms the greater part of 

 the visceral nuiss. The reproductive organ varies greatly according to the season, and forms most of what is known as the "fat" of the 

 oyster. 



There are no accessory organs of reproduction, and the position, form, and general appearance of the reproductive organ is the same 

 in both sexes. There is no characteristic by which a male oyster can be distinguished from a female, without microscopic examination. 

 As tho reproductive organ has an op ning on each side of the body, it is usually spoken of as double, but in the adult oyster it forms one 

 continuous mass, with no trace of a division into halves, and extends entirely across the body and into all the bends and folds of the 

 digestive tract. 



Eeproduction and embryology. — All accouut of the liie-liistoi'y of the oyster shonhl begin witli the 

 begiuniug — the egg— out of which this iiiolhisk, like everything else from nuissel to man, is born. And in this 

 matter of oyster-breeding, I mnst rely npon and again quote at length the researches of Dr. Brooks, since he is 

 easily in advance of all stndeiits in his knowledge of this sultject. During the summer of 1880, at his seaside 

 laboratory, Crisfield, Marjland, and subsequently. Dr. Brooks made microscopic studies on the embryology of the 

 oy.ster, which were publislied, with figures, in the Re])ortof the Maryland Fi.sheries Commission for 1880, and in the 

 Memoirs of the Johns Hopkins University. These investigations were of the most painstaking description, and 

 may be accepted as satisfactorily portraying the true method of reproduction of the American oyster, Ontrca 

 virfiiniana, although sho\\ing it to be essentially different from that of tUe oyster of Europe O.strca eduKs. It is my 

 duty as well ;is pleasure, conseqtiently, to set forth with as great accuracy as condensation and a popular treatment 

 of the subject will permit, the statements of Dr. Brooks. 



If several oysters tire opened during the breeding-season, which varies, as will hereafter be shown, a few will 

 be found with the reproductive organ greatly distended and of a uniform opaque white color. These are oysters 

 which are spawning or ready to spawn, that is, to discharge their eggs. Sometimes the ovaries will be so gorged 

 tliat tbe ripe eggs will ooze from the openings of the oviducts before the mass is quite at the point ot being dischitrgetl. 

 If the point of a knife be ])ushed into the swollen ovary, a milk-white fluid will flow out of the cut. Mixing a little 

 of this with seti water and placing it on a slide unilerneath a cover, a lens of 100 tliameters will show, if the 

 specimen is a female, " that the white fluid is almost entirely made up of irregular, pear-shaped, ovarian eggs 

 (Figure 49), each of which contains a large, circular, transparent geriuinative vesicle, surrounded by a layer of 

 granular, .slightly opaque .\olk." Perfei^ttly ripe eggs will be seen to be clean, sharply defined and separate from 

 each other. If the specimen be male, a glance through the microscope shows something (piite different from tlio 

 fluid of a female. " There are no large bodies like the eggs, but the fluid is tilled with innumerable numbers of minute 

 granules (Figure 48), which arc so small that they are barely visible when magnified one hundred diameters. They 

 are not uniformly distributed, but are iiuich more nnmerous at some ])oiiits than tit others, and for this reason the 

 fluid has a cloudy or curdled appearance. By selecting a place where the granules are few and pretty well scattered, 



