328 L. V. HEILBRUNN. 



sure forces water to enter the eggs and the membrane bursts- 

 In many instances the ruptured membrane could be seen at one 

 side of the egg. Sometimes exovates were produced. Various 

 dilutions were employed, from pure distilled water to a mixture 

 of I part of distilled water to 2 parts of sea-water. In one 

 experiment eggs were exposed to distilled water for 40, 60 and 

 80 seconds and then returned to sea-water. All three exposures 

 were successful. The 40 second exposure was not counted, the 

 60 second exposure showed 51/100 polar bodies and the 80 second 

 exposure 52/100 polar bodies. The controls were normal and 

 over 200 eggs which were counted showed no signs of maturation. 

 All the exposures showed some signs of cleavage. One egg 

 reached a stage with about 16 cells. In another experiment 

 eggs were placed into 30 c.c. of sea-water plus 15 c.c. of distilled 

 water. Of these eggs 13/50 showed polar bodies. 



THE SIGNIFICANCE OF CORTICAL CHANGE. 



It has been shown that three types of cortical change can be 

 produced in the Cumingia egg. All of these free the egg from 

 the restraint of a stiff vitelline membrane. This release from 

 restraint may then be thought of as the essential feature of 

 cortical change and as the direct cause of maturation. When it 

 occurs maturation follows; without it no maturation takes place. 



It might be argued that all of the types of cortical change 

 have some other common effect besides the one mentioned. 

 Perhaps they all directly produce an increase of oxidations, 

 which then causes maturation to follow. This would be a diffi- 

 cult relation to conceive of chemically. Moreover there is experi- 

 mental evidence that maturation does not depend on an increase 

 of oxidations. 



The supporters of the oxidation theory of initiation of develop- 

 ment have always held that dilute cyanide solutions check 

 oxidations. Thus Loeb, '13, states on p. 26: "It has long been 

 known that the oxidations in the cell can be prevented by the 

 addition of a little potassium cyanide, even when oxygen is 

 present. I have found that the addition of 0.5 c.c. of a 1/20 

 per cent. KCN solution to 50 c.c. of sea-water is sufficient to stop 

 almost immediately the effect of the spermatozoon in the fertilized 

 sea-urchin egg." Such a solution is 0.0005 P er cent. 



