36 LIBBIE H. HYMAN. 



greatly indebted to the director of the fisheries station for his 

 kindness in supplying me with an abundance of material. Cod 

 eggs in all stages of development were obtainable at any time. 



In studying the gradients the eggs were placed in watch glasses 

 which were filled with the toxic solution, and observed under the 

 low power of the compound microscope. Sometimes the watch 

 glasses were filled full and covered with a circular piece of thin 

 glass with the exclusion of air. It was found, however, advisable 

 in most cases to leave the watch glasses uncovered since it was 

 frequently necessary to turn the eggs with a needle in order to 

 bring all parts into view. The eggs of the cunner and the cod 

 are pelagic floating eggs but very soon after being placed in the 

 solution they become opaque and sink to the bottom. Since the 

 eggs in all three species rest upon the bottom of the watch glass 

 it is easy to turn them into any desired position by mean of a. 

 needle. 



For the disintegration of the embryos of Tautogolabrus, solu- 

 tions of potassium cyanide in sea-water were employed, in con- 

 centrations of i/ioo mol. or stronger. When work was begun on 

 the eggs of Fundulus it was immediately discovered that potas- 

 sium cyanide was useless for the purpose. Apparently the egg 

 membranes of this fish are impermeable to cyanide for the 

 embryos will live and their hearts will continue to beat for very 

 long periods in relatively concentrated cyanide solutions. It was 

 found that anaesthetics and acids would penetrate the eggs of 

 Fundulus very readily and stop the heart beat within a few 

 minutes ; but in none of these substances could the disintegration 

 gradients be observed for they seemed to coagulate the embryo 

 and it was consequently impossible to determine the time of 

 death of different levels. Finally after fruitless trials of many 

 substances, it occurred to me to try ammonium hydroxide, as it 

 is well-known that this substance penetrates invertebrate eggs 

 readily. It proved to be entirely satisfactory and was thereafter 

 exclusively employed for the study of the gradients of Funduhis 

 and the cod. In making ammonium hydroxide solutions several 

 drops of the pure concentrated solution were added to about fifty 

 c.c. of sea-water ; the sea-water was then shaken thoroughly and 



