402 



A. J. GOLDFARB. 



with further age. The rate of cleavage follows a similar cycle; 

 the rate of cleavage and the total cleavage increased with the age of the 

 germ cells until they were 280 minutes old, after which the rate was 

 retarded and the total cleavage declined. 



Arbacia. 



With Arbacia eggs the rate of cleavage was ascertained by 

 noting the per cent, of the eggs that reached the 4-cell stage in 60 

 minutes. The data are shown in Table VIII. 



TABLE VII I. 



SHOWS CHANGE IN RATE OF CLEAVAGE FROM THE PER CENT. OF EGGS THAT REACH 

 THE 4-CELL STAGE IN 60 MINUTES. Arbacia. 



In Arbacia as in Toxopneustes the total cleavage decreased and 

 the early division process was increasingly retarded with in- 

 creasing age of the germ cells. In experiment 3, for example, the 

 eggs of 5 females were tested when their germ cells were 1^2 hours 

 old, and 59 per cent, of the eggs reached the 4-cell stage in i hour. 

 When the germ cells were 5 hours old only 38 per cent, reached 

 the 4-cell stage in the same time. In experiment i and 2, older 

 eggs were used. The results were even more striking and in 

 entire accord with the preceding experiments. 



