THE OYSTER-INDUSTRY. 213 



riirtlier than this, he discovered tliat although the American oyster seems well adapted to follow the European 

 species, and various other marine and fresh-water Lamellibranchs, to dra-w into its mantle chamber, with the 

 sea- water, the spermatozoa discharged from the mantle chambers of neighboring oysters, and thus to bring about 

 the fertilization of the eggs inside the cavity of the shell, this does not seem to occur. He aflirms this very positively, 

 and scientilic men generally have accepted the conclusious as facts. I quote the words of one pnragraph relating 

 to it : 



I have carefully searched the gills and mantles of more than a thousand oysters, at a time wlien the reproductive organs were plainly 

 Been to bo discharging their ripe contents, an<l have not found a single fertilized egg or embryo in any part of the mantle chamber, in or 

 on the gills, or anywhere else inside the shell. This negative evidence, together with the fact that the eggs can be hatched .-iftcr they 

 have lieeu artificially removed from the ovaries, seems sufficient to prove, iu the absence of all evidence to the contrary, that the eggs of 

 the A)ncrican oyster undergo development in the open ocean." 



That is to say, during all the period when the young of the European oyster is l)eing safely nurtured inside the 

 niautlecavity of its parent, and protected from all harm by its strong shells, our infant oysters swim at large in 

 open ocean— if lucliy enough to get himself born at all from the egg which is sent abroad unfertilized, to meet a 

 chance male cell and so become impregnated and start into life, if fortune favors. 



Experiments in artificial fertilization. — As has been hinted. Dr. Brooks spent much of his time and 

 eSbrts at the laboratory in experimenting upon the artilicial fertilization of oysters, by mixing eggs extracted from 

 a female ^vith spermatozoa from a male. Ue found it an easy matter to secure their union, and made his 

 embryological studies from eggs and embryos thus cultivated, in a watch crystal or in a glass beaker. He gives 

 minute directions as to the proper method for repeating these experiments, which those having a microscope can 

 easily undertalce, but which may be omitted as not pertinent here. 



DeveloPxAIENt of the youno oyster.— The next step, having got the eggs, or learned their nature, is to 

 examine theii' fertilization and development. Dr. Brooks writes: 



The body of the oyster, like that of all .animals, except the very simplest, is made np of organs, snch as the he.art, digestive organs, 

 gills, and reproductive organs, and these organs are at some period iu the life of the oyster made up of microscopic cells. Tho 

 eggs shown in Figures 49 and 5:5 will answer to illustrate the character of the cells which compose the body. Each of these consists 

 of a layer of proto])lasm aronnd a central nucleus, which, in the egg, is a large, circular, tr.ansparent body known .as the germinativo 

 vesicle. Each cell of the body is .able to absorb food, to grow and to multiply by division, .and thus to contribute to, the growth of the 

 organ of which it forms a part. The ovarian eggs are simply the cells of an organ of Hie body, the ovary, .and they differ from tho ordinary 

 cells only in being much larger and more distinct from each other ; and they have the power, when detached from the body, of growing 

 and dividing up into cells, which shall shape themselves into a new organism like that from whose body the egg came. Most of the steps in. 

 this wonderful process may be watched under the microscope, and owing to the ease with which the eggs of the oyster may be obtained, 

 this is a very good egg to study. 



About fifteen minutes after the eggs are fertilized they will be found to be covered with m.ale cells, as shown in Figure 51. In about 

 an hour tho egg will be found to have changed its shape and appearance. It is now nearly spherical, as shown in Figure 1, and the 

 germinative vesicle is no longer visible. The male cells may or may not still be visible upon the outer surface. In a short time a littlo 

 transparent point makes its appearance on tho surface of the egg, and increases in size, and soon forms a little projecting transjiarcnt 

 knob — thir j>olar globule — which is shown in Figure :{ and in succeeding figures. 



Recent investigations tend to show, that whiU-. tlvso changes are taking place, one of the male cells penetrates the protoplasm of tho 

 egg and unites with the germinative vesicle, which docs not disappear, but divides into two parts, one of which is pushed out of the egg 

 and becomes the pol.ar globule, while the other remains behind and becomes the nucleus of the developing egg, but changes its appearance 

 so that it is no longer conspicuous. The egg now becomes pear-shaped, with the polar globule at the broad end of the pear, and this end 

 soon divides into two parts, so that the egg ( Figure G) is now made of one large mass and two slightly smaller ones, with the polar globule 

 between them. 



The later history of the egg shows that .at this early stage the egg is not perfectly homogeneous, but that the protoplasm which is to 

 give rise to certain org.ans of the body has separated from that which is to give rise to others. 



If tho egg, at the stage shown iu Figure G, were split in the plane of the paper, we should have what is to become one half of the 

 body in one part and the other half in the other. The single spherule at the small end of the pear is to give rise to tho cells of the digestive 

 tr.act of the adult, and to those organs which are to be derived from it, while the two spherules at tho small end are to form the cells of the 

 outer wall of the body and the organs which are derived from it, such as tho gills, the lips, and the mantle, and they are also to give rise 

 to the shell. The upper portion of tho egg in this and succeeding figures is to become the ventral surface of the adult oyster, and the 

 stirface which is on the right side in Figure 6, is to become the anterior end of the body of the adult. The figure, therefore, shows the half 

 of the egg which is to become the loft half of the body. The upper portion of the egg soon divides up into smaller and smaller spherules 

 until at the stage shown in Figures '24, 2o, and lUi w(! have a layer of small cells wrapped arouml the greater jtart of the surface of a single 

 large spherule, and the series of figures shows that the latter is the spherule which is below iu Figure (i. This spherule now divides up into 

 a layer of cells, and at the same time tho egg, or rather the embryo, becomes fiattened from above downward, and assumes the shape of a 

 flat ov.al disk. Figures 29 and 30 are views of the upper and lower surface of the embryo at about this time. In a sectional view, Figure 

 :n, it is seen to be made up of two layers of cells; .an upper layer of small t.ransi)arent cells, re, which are to form the oiiter wall of tho 

 body, .and which have been formed by the division of the spherules which occupy the upper end of the egg in Figure 2.5, .and a lower layer 

 of much larger, more opaque cells, g, which are to become the walls of the stomach, and which have been formed by the division of the 

 large spherule, a, of Figure 20. 



•Writing concerning his work in 1881, Mr. .Tohn A. Ryder remarks: "No evidence to show that our oyster is hermaphrodite was 

 found during the entire season, nor were my searches for embryo or eggs in the mouth or iu the gills, more successful than those carried 

 on two years before by Professor Brooks. Tliere is no doubt whatever that the oyster of Europe nurses its young on its mantle or gills 

 for some time, nor can we well question the very high authority of Mcibius, for saying th.at in most cases tho sexes are .separate, and that 

 only ime kind of products, viz, citlier eggs or spermatozoa, are at any time found iu the geuirat ivc organ.s. Lacaze Duthier's ob.servations 

 seem to couUiui the conclusious of Mobius." — Bi'poyI of T. B. Ferguson, a commissioner of Jisheritu of Mari/luiul, ■hitUKirij, 1881, p. 14. 



