XXIX 



ON THE ARTIFICIAL PRODUCTION OF NORMAL LAR- 

 VJE FROM THE UNFERTILIZED EGGS OF THE SEA- 

 URCHIN (ARBACIA) 1 



I. INTRODUCTOEY REMARKS 



EIGHT 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 



i American Journal of Physiology, Vol. Ill (April 1, 1900), p. 434. 



576 



