THE ELECTROLYTE CONTENT OF THE SEA URCHIN 



AND STAR FISH EGG. 



IRVINE H. PAGE. 1 



The sea urchin (Arbacia punctulata) and star fish (Asterias 

 forbesii) eggs have been the subject of very extensive morpho- 

 logical and physiological research. Since both of these types of 

 investigation are intimately related to the chemical composition 

 of the egg, the following analyses of the electrolyte content of 

 these two Echinoderm ova are presented. 



* 



EXPERIMENTAL METHODS. 



Arbacia eggs were removed from the ovaries, strained through 

 cheese cloth, centrifuged until as much sea water as possible was 

 removed. The egg mass was then almost solid. The surface 

 layer was then quickly washed over with a few cubic centimeters 

 of distilled water, not sufficient to cause cytolysis but enough to 

 remove any slight amount of sea water remaining on the surface. 

 A sample of the egg mass was removed to determine the number 

 of eggs, the volume of the egg mass determined, and the mass 

 dried at 100 degrees C. in a Freas oven until constant in weight. 

 Samples of this dried material were then ashed in a platinum 

 crucible in an electric crucible furnace, a few drops of HNOs being 

 added to aid the ignition. The ash was weighed and dissolved 

 in 5 cc. of N/io HC1, made up to 25 cc., and the SiO 2 centrifuged 

 out. Aliquot portions were then used for the special analytical 

 procedures. 



Calcium. 5 cc. of the filtrate were brought to about pH 6.0, 

 2 cc. saturated ammonium oxalate added and the centrifuge tube 

 in which the solution was contained vigorously "rubbed down" 

 with a stirring rod. After 12 hours the tube was centrifuged and 

 the precipitate washed three times with hot water. The calcium 

 was then determined by the usual ignition method as CaO and as 

 an alternative procedure dissolved in 4N H2SO4 and titrated hot 

 with A T /ioo KMnO 4 . 



1 Contribution from the Research Division of Eli Lilly and Company, Marine 

 Biological Laboratory, Woods Hole. Mass. 



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