2J4 HELEN DEAN KING. 



extruded, approximately equal portions of the eggs were trans- 

 ferred into finger bowls which contained loo c.c. of the solution 

 to be tested. As a control by which to judge of the effects of 

 the solutions, one portion of the eggs was allowed to develop in 

 100 c.c. of normal sea-water. The various experiments were 

 made in a similar manner and the eggs were kept under like 

 conditions of light and of temperature during their development 

 in order that the results of the experiments might not be affected 

 by environmental conditions other than those that were being 

 studied. 



A. EXPERIMENTS WITH THE EGGS OF Arbacia punctulata. 



As the breeding season of Arbacia is near its close the latter 

 part of July, only a small number of eggs suitable for experimental 

 purposes could be obtained. All of the eggs used were presum- 

 ably in a normal physiological condition, as at least 90 per cent, 

 of those in the control cultures developed in a normal manner 

 and became plutei. 



In each series of experiments observations were made at fre- 

 quent intervals on the living embryos. These observations were 

 later supplemented by a microscopic study of various lots of 

 material that had been fixed in corrosive sublimate and stained 

 with Heidenhain's iron-haematoxylin or with Delafield's hacma- 

 toxylin followed by eosin. 



Cystin (C6Hi2OiN 2 S2). As this substance is very insoluble in 

 cold sea-water, the solution used in the first experiment that 

 was made was prepared in the following way: A quantity of the 

 pure crystalline salt was placed in a flask of sea-water heated to 

 40 C. The mixture remained at this temperature for one half 

 hour and was then sealed and set aside. After three days the 

 solution was filtered, to remove the undissolved cystin, and used 

 within a few hours. 



A lot of Arbacia eggs was fertilized at 11.45 A.M. on the 

 morning of July 14, 1909, and a portion of them was placed in tin- 

 saturated solution of cystin at 12.15 I'-M. These eggs were 

 found to be segmenting in a normal manner when division of tin 

 eggs in the control culture took place at 12.50 P.M., and for some 

 hours the eggs of both cultures seemed to be developing at about 



