XXIX 
ON THE ARTIFICIAL PRODUCTION OF NORMAL LAR- 
V# FROM THE UNFERTILIZED EGGS OF THE SEA- 
URCHIN (ARBACIA)' 
I. INTRODUCTORY REMARKS 
E1eutT years ago I published the results of some experi- 
ments on the effects of an increase in the concentration of 
sea-water upon the segmentation of the egg. I had found 
that the addition of a small quantity of NaCl to sea-water 
retarded segmentation in the egg of the sea-urchin. By 
increasing the concentration a point was soon reached where 
no further segmentation occurred. If one carefully selects 
the minimum increase in the concentration which is able to 
prevent the segmentation of the egg, and the eggs be kept 
in this solution for one or more hours, a peculiar phenome- 
non occurs. When put back into normal sea-water the eggs 
do not segment into two, four, eight cells, and so on, succes- 
sively, but begin to divide into more than two cells very 
soon after being brought back into the sea-water. The 
longer the egg is kept in concentrated sea-water, the greater 
is the number of cells into which it breaks up at once. I 
repeatedly saw an undivided egg go into a morula stage 
within fifteen minutes after it was put back into the normal 
sea-water. I did not make a thorough histological examina- 
tion of these eggs. Dr. Conklin was kind enough to stain a 
lot of eggs that had been in concentrated sea-water and 
which showed no trace of segmentation. ‘Some of these 
eggs showed very distinctly from four to about thirty nuclei; 
in other eggs the segmentation of the nucleus was not so 
perfect. The nucleus, extremely large, seemed to consist of 
1 American Journal of Physiology, Vol. III (April 1, 1900), p. 434. 
576 
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