1202 OYSTERS, AND ALL ABOUT THEM. 



entire water. When the embryos are at this stage their 

 number may be estimated in the following manner : The 

 whole mass of embryos is carefully scraped from the beard 

 of the mother oyster by means of a small hair-brush. 

 The whole mass is then weighed, and afterwards a small 

 portion of the mass. This small portion is then diluted 

 with water or spirits of wine, and the embryos portioned 

 out into a number of small glass dishes, so that they can 

 be placed under the microscope and counted. Thus, 

 knowing the weight of the small portion and the number 

 of embryos in it by count, we can estimate the total num- 

 ber of embryos from the weight of the entire mass, which 

 is also known. In this manner I estimated the number of 

 embryos in each of five full-grown Schleswig-Holstein 

 oysters, caught in August, 1869, and found that the average 

 number was 1,012,955. (a) 



Dr. Brooks tells us that if several oysters are opened 

 during the breeding season, .... a few will be 

 found with the reproductive organ greatly distended, and 

 of a uniform opaque white colour. These are oysters 

 which are spawning or ready to spawn, that is, to discharge 

 their eggs. Sometimes the ovaries will be so gorged that 

 the ripe eggs will ooze from the openings of the oviducts 

 before the mass is quite at the point of being discharged. 

 If the point of a knife be pushed into the swollen ovary, 

 a milk-white fluid will flow out of the cut. Mixing a little 

 of this with sea-water, and placing it on a slide underneath 

 a cover, a lens of 100 diameters will show, if the specimen 

 is a female, " that the white fluid is almost entirely made 

 up of irregular, pear-shaped, ovarian eggs, each of which 

 contains a large, circular, transparent germinative vesicle, 



(a) "The Oyster and Oyster Culture," pp. 10-14. 



