CHAPTER 11 



The mature egg, unfertilized and fertilized 



a. Quantity of Eggs in an Arbacia 



The number of eggs obtained from one Arbacia varies considerably with 

 the season. Even at the height of the season, some females have many 

 more eggs than others. Usually, the eggs obtained from one female in 

 the usual way, by allowing them to ooze out of the excised ovaries and 

 then filtering through cheesecloth, will well cover the bottom of a 

 finger bowl in a thin layer; from exceptionally good females, they cover 

 the bottoms of two finger bowls. When allowed to settle for several 

 hours by gravity, the volume of the eggs from an exceptionally good 

 female amounts to 5 cc. With light centrifuging, this amounts to 3 cc, 

 but many are now without jelly. The 5 cc. of settled eggs with jelly 

 contain approximately 4,000,000 eggs since each egg has a volume of 

 1,260,300 [i^ (diameter, egg 74 [a + jelly 60 11, without interspaces be- 

 cause the jelly of adjacent eggs is contiguous). The volume of the settled 

 eggs is about equal to the volume of eggs left in the ovaries. One 

 Arbacia, then, contains about 8,000,000 eggs. The same figure has been 

 arrived at for the number of eggs shed either by KCl or by the electrical 

 method. MacBride (1906, p. 529) states that a well grown Echinus 

 esculentus contains 20,000,000 eggs; this compares fairly well with the 

 figures for Arbacia since Echinus esculentus is a very much larger animal. 



Quantity of eggs in i cc. settled by gravity (E. B. Harvey) 



Eggs with jelly 800,000 (vol. per egg 1,260,000 u.^; there are no 



interspaces, eggs are contiguous). 

 Eggs without jelly 3,500,000 (vol. per egg 212,200 (x^; allowing 26% 



for interspaces). 

 Eggs without jelly 4,700,000 (no allowance for interspaces). 

 Other figures have been given by Krahl (1950, p. 177). 

 Eggs per 10 c.mm. 46,500 



Eggs per wet gram 4,300,000 



Eggs per mg. dry weight 1 7,600 



