THE CHANGE IN VOLUME OF ARBACIA AND ASTERIAS 

 EGGS AT FERTILIZATION. 1 



OTTO GLASER. 



In my paper on the initiation of development, Glaser (13), 

 I stated that the eggs of Arbacia punctulata and Asterias forbesii 

 are smaller in volume after fertilization than before. In the 

 pages that follow I wish to present the evidence for this assertion 

 in some detail, since for the present at least, it must stand alone. 

 Strongylocentrotus (purpuratus?) shows no recognizable loss of 

 volume according to Loeb ('08) but this result does not contradict 

 mine. The loss depends on several conditions, and in Asterias 

 is much greater than in Arbacia. This suggests the possibility 

 of forms in which it may easily be too small to measure. The 

 measurements of McClendon ('10), also, do not contradict mine, 

 although they seem to show that the very eggs I worked with, 

 on fertilization lose in a molar solution of dextrose, but remain 

 constant, or even gain a little in sea water. The evidence consists 

 in the determination of the diameters of 19, 20, 10 and u eggs 

 respectively. The great variability of the ova of Arbacia 

 punctulata, however, proves that reliable results can be gotten 

 from a small number of eggs, only when the identical ones are 

 measured before and after fertilization. 



Careful tracings were made at known magnifications with the 

 aid of a camera lucida, and a crow-quill pen, on paper of known 

 weight. On the assumption that the eggs are spheres, and that 

 one is really drawing their great circles, the areas of the outlines 

 obtained in this manner, were first determined by means of a 

 planimeter, and afterwards by carefully cutting them out and 

 weighing the discs. For enlargements of 740 diameters both 

 methods gave identical results, but for the smaller magnifications 

 the method of weighing proved more reliable. For this reason, 

 in the comparisons of fertilized with unfertilized eggs, only data 



1 From the Marine Biological Laboratory at Woods Hole, and Zoological 

 Laboratory of the LTniversity of Michigan. 



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