200 FISHERIES OF THE UNITED STATES. [10] 



were oozing from the openings of the oviducts; others where the ovaries 

 were half emptied, and others which had discharged almost all their 

 eggs, and others at all the intermediate stages, but in no case did I find 

 a single developing egg inside the shell of the parent. 



"ARTIFICIAL IMPREGNATION OF THE OYSTER EGGS. 



"If a number of oysters are opened during the breeding season, a 

 few will be found with the reproductive organ greatly distended and of 

 an uniform pure opaque white color. These are oysters which are 

 spawning or nearly ready to spawn. 



"If the point of a knife be pushed into the reproductive organ a milk- 

 like iiuid will ooze out of the cut, and a little of it may be taken up on 

 a knife blade and transferred to a glass slide for examination. The drop 

 of fluid should be thoroughly mixed with a drop of sea water and placed 

 on the slide, and gently covered with a cover-glass, and examined with 

 a magnifying power of about one hundred diameters. If the specimen 

 is a female, this power will show that the white fluid is almost entirely 

 made up of irregular pear-shaped ovarian eggs (Fig. 49), each of which 

 contains a large circular transparent germinative vesicle surrounded 

 by a layer of granular slightly opaque yolk. It is almost impossible 

 to describe the slight differences which distinguish the perfectly ripe 

 egg from those which are nearly ripe but not capable of fertilization, 

 although a very little experience will enable one to tell whether it is 

 worth while to attempt the fertilization of the eggs of any given female. 



"When the drop of fluid is thoroughly mixed with the sea water, 

 the eggs should appear clean, sharply defined, separate from each other, 

 and pretty uniformly distributed through the drop, as shown in the 

 figure. If they adhere to each other, or if their outlines are indistinct, 

 or if their is much finer granular matter scattered between the eggs, it 

 is probable that the attempt at artificial fertilization will at best be 

 only partially successful. 



"When a perfectly ripe female is found, it should be set aside and 

 the search continued for a male. The question of the sex of the oyster 

 has long been a matter of dispute, and the subject will be fully dis- 

 cussed in another place. All that concerns us now is to know that for 

 all practical purposes the sexes are separate in the European as well 

 as the American oyster. At the breeding season each individual is 

 either exclusively a male or exclusively a female. Out of several thou- 

 sand which I examined, I have not found one which contained both eggs 

 and male cells, aud all the best authorities upon the European oyster 

 make the same statement, although there is some reason for the belief 

 that an oyster may give rise to eggs one season and to male cells another 

 year. When a drop of the milky fluid from a ripe male is mixed with 

 a little sea water and examined with a magnifying power of one him 

 dred diameters, it is seen at a glance to be quite different from the fluid 

 of a female. There are no large bodies like the eggs, but the fluid is 



