CHARLES D. SNYDER. 



When mature eggs of Asterina miniata are treated with sperm, 

 the egg-cytoplasm during early stages of cleavage has an average 

 diameter of 17.7 and the fertilization membrane one of 21 mm. 

 This is shown in the table. 



EGGS OF Asterina Miniata FERTILIZED WITH NORMAL SPERM. 



The mean diameters in these observations are 17.1 for the egg-cytoplasm and 

 22.5 for the membrane. The averages thus show less deviation than do the mean 

 numbers. The amount of shrinking of the egg-cytoplasm comparing the mean 

 diameters before and after fertilization is n.i per cent.; comparing the average 

 diameters it is 7.8 per cent. 



During the early stage of normal fertilization, then, the eggs of 

 Asterina miniata may be said to show a marked shrinking of the 

 egg-cytoplasm. 



These figures are of the same order as Glaser (1914) observed 

 *or the reduction in diameters of just fertilized Arbacia eggs (from 

 x.4 to 14.5 per cent.) and Asterias eggs (from 10 to 17 per cent.) ; 

 and Okkelberg 5 in volume reduction of eggs of the brook lamprey, 

 13.4 per cent. Just lately (1924) Glaser 1 repeated the measure- 

 ments of Arbacia, using an improved method in order to prevent 

 possible flattening of eggs before the membrane has been elevated 

 (first suggested by Reighard, see Okkelberg, loc. cit., p. 97, 

 footnote 2), and finds that the percentage reduction of diameter 

 is less than in his earlier work, but still a demonstrable mean of 

 3 per cent. 



4. In spite of the meagerness of observations (the lack of 

 measurements on the sand-dollar egg during the earliest stages 

 following insemination, the lack of a more perfected treatment to 



6 Okkelberg, "Volumetric Changes in the Egg of the Brook Lamprey . . . after 

 Fertilization," BIOL. BULL., Vol. XXVI., pp. 92-99, 1914. 



