202 FISHERIES OE THE UNITED STATES. [18] 



we allow one-half for foreign matter and errors of measurement, and 

 for imperfect contact between the eggs, we shall have more than nine 

 millions as the number of eggs laid by an oyster of average size, a num- 

 ber which is probably less than the true number. 



" Mobius estimates the number of eggs laid by an average European 

 oyster at 1,012,925, or only one-ninth the number laid by an ordinary 

 American oyster, but the American oyster is very much larger than the 

 European, while its eggs are less than one-third as large, so the want 

 of agreement between these estimates does not indicate that either of 

 them is incorrect.* Another estimate of the number of eggs laid by 

 the European oyster is given by Eyton (History of the Oyster and 

 Oyster Fisheries, by T. C. Eyton. London, 1858). He says, p. 24, that 

 there are about 1,800,000, and therefore agrees pretty closely with 

 Mobius. 



"An unusually large American oyster will yield nearly a cubic inch 

 of eggs, and if these were all in absolute contact with each other, and 

 there were no portions of the ovaries or other organs mixed with them, 

 the cubic inch would contain 500 3 , or 125,000,000. Dividing this, as 

 before, by two, to allow for foreign matter, interspaces, and errors of 

 measurement, we have about 60,000,000 as the possible number of eggs 

 from a single oyster. 



" Although each male contains enough fluid to fertilize the eggs of 

 several females, there does not seem to be much difference in the num- 

 ber of individuals of the two sexes. When a dozen oysters are opened 

 and examined there may be five or six ripe females and no males, but 

 in another case a dozen oysters may furnish several ripe males but no 

 females, and in the long run the sexes seem to be about equally numer- 

 ous. Oystermen believe that the male may be distinguished from the 

 female by certain characteristics, such as the presence of black pigment 

 in the mantle, but microscopic examination shows that these marks 

 have no such meaning, and that there are no differences between the 

 sexes except the microscopic ones. It is not necessary to use the micro- 

 scope in every case, however, for a little experience will enable a sharp 

 observer to recognize a ripe female without the microscope. If a little 

 of the milky fluid from the ovary of a female with ripe or nearly ripe 

 eggs, to be taken upon the point of a clean, bright knife-blade, and 

 allowed to flow over it in a thin film, a sharp eye can barely detect the 

 eggs as white dots, while the male fluid appears perfectly homogeneous 

 under the same circumstances, as do the contents of the ovary of an 

 immature female, or one which has finished spawning. When the eggs 

 are mixed with a drop of water, they can be diffused through it without 

 difficulty, while the male fluid is more adhesive and difficult to mix 



*" Mobius' measurement, from 15 to 18 millimeters, is given (Austern und Austern- 

 wirtschaft, 1877), as the diameter, not of the egg, but of the embryo, but his figures 

 show that the European oyster, like the American, does not grow much during tha 

 early stages of development, but remains of about the same size as the egg." 



