EGG-VOLUME AND FERTILIZATION MEMBRANE. 



CHARLES D. SNYDER. 



The question of fertilization and egg-volume seems to come up 

 periodically for renewed research and discussion in spite of the 

 papers already written on the topic. 1 In view of the disagree- 

 ment as to the facts of volume changes at the moment of fertili- 

 zation the writer wishes to submit the following evidence that 

 was put in a paper in December, 1904, from observations made in 

 that year on two species of echinoderms, and that hitherto has 

 not been published. The work was done at the Timothy Hopkins 

 Sea-side Laboratory of Stanford University, California. 



The microscope images of the eggs were projected by a camera 

 lucida, and outline drawings were made of their greatest diame- 

 ters. Upon each sheet of drawings a stage micrometer scale was 

 also projected and drawn. The magnification was uniform 

 throughout. The diameters given in sections 1-4 inclusive, of 

 this paper, are of these drawings, and should be divided by 1 10 in 

 each case to get the approximate natural diameter. 



i. Echinarachnius eccentrical Eggs made to develop parthe- 

 nogenetically by treatment with hypertonic salt solution are 

 known to shrink and then to swell again upon return to normal 

 sea-water. Mature eggs of Echinarachnius eccentrica put in 

 optimum hypertonic solution for i| hours were observed to shrink 

 from a mean normal diameter of 13.27 to a mean diameter of n.6 

 mm. After return to normal sea-water for I hour the eggs showed 

 diameters ranging from 12.86 to 13.18 mm. By the time cleavage 

 began, and the eggs were still in I and 2-cell stages, the diameters 

 ranged between 14 and 16 mm. ; when in stages varying from the 

 4-cell to the morula stage, the diameters ranged between 14.5 and 

 18 mm. These measurements refer to the egg-cytoplasm, no 

 membranes appearing on eggs so treated. 



1 For review of the literature and discussion of the problem see Lillie, F. R., 

 "Problems of Fertilization," Chicago, 1919, pp. 147-154; also Glaser, Otto: 

 "Fertilization, Cortex and Volume," BIOL. BULL., Vol. XLVIL, pp. 274-283, 1924. 



2 Thanks are due to Professor Harold Heath, who kindly identified this species of 

 sand-dollar for the writer. 



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