408 A. J. GOLDFARB. 



Change in Cleavage. 



When freshly liberated eggs of Hipponoe and Toxopneustes in 

 good physiologic condition were fertilized under the given op- 

 timum conditions at successive ages the total cleavage increased 

 for a time and subsequently decreased, 1 and in extreme ageing 

 none of the eggs segmented. 



Cleavage then is an additional index of the degree of senescence 

 or physiologic deterioration of the eggs. 



There were two series of experiments, one in which the eggs and 

 sperm aged synchronously, and the other in which they aged 

 asynchronously. In both series the rate of decrease in cleavage 

 with age was several times greater in Toxopneustes and Hipponoe 

 than in Arbacia. This difference in rate of senescence as in rate 

 of membrane formation, loss of jelly and change in size is due 

 largely to differences in temperature, as well as to differences in 

 HO concentration of the sea water, and to protoplasmic dif- 

 ferences of the eggs. 



When both germ cells aged synchronously the apparent 

 longevity was about 1 1 hours for Toxopneustes and about 28 

 hours in Arbacia. 



In asynchronous matings a more definite idea was obtained of 

 the changes in the egg alone and in the sperm alone. When 

 freshly liberated sperm were used to fertilize the eggs (of a female) 

 at varying 'ages, with the precautions indicated in the text, the 

 eggs showed progressively decreasing per cent, of cleavage (in 

 Arbacia}, but the rate of decrease was very much slower than 

 when both germ cells a^ed synchronously. The decrease may be 

 divided into three periods, the first a period of small decrease 

 (about the first 20 hours in Arbacia) the second, a period of 

 rapid and large decrease (between the 2Oth and 4Oth hour), and 

 the third, a period of small decrease (between the 4Oth and 8oth 

 hour in Arbacia}. 



Eggs in poor physiologic condition at the time of liberation 

 deteriorated at a conespondingly greater rate than physi- 

 ologically good eggs. 



1 Freshly liberated eggs, of freshly collected Arbacia, in good physiologic condi- 

 tion, gave a maximum or nearly maximum cleavage and with ageing there was a 

 direct decreasing total. 



