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HANDBOOK OF mVERTEBRATE ZOOLOGY. 



of it may be taken upon 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 ex- 

 amined with a magnifying power of about one hundred 

 diameters. If the specimen is a female, this power will 

 show that the fluid is almost entirely made up of irregular 

 pear-shaped ovarian eggs (Fig. 156), each of which con- 

 tains a large circular transparent germinative vesicle sur- 

 rounded 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. 



Fig. 156-172. — The embryology 

 of the oyster. (All the figures 

 were drawn from nature by W. K. 

 Brooks, and unless the contrary is 

 stated they are magnified two hun- 

 dred and fifty diameters. ) 



Fig. 156. — Eggs from the ovary 

 of a ripe female, magnified one hun- 

 dred diameters. 



Fig. 156. 



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 there 

 is much fine granular matter scattered between the eggs, 

 it is probable that the attempt at artificial fertilization will 

 at best be only partially successful. 



