ACCELERATION OF RATE OF CELL DIVISION. 361 



quantity of stones and sand from the tidal flat where they were 

 first secured. Although they would at length become exhausted, 

 no difficulty was experienced for some days in getting them to 

 produce eggs. 



The eggs are laid in a jelly mass which has the appearance of a 

 short piece of narrow but very thick ribbon. It is of rather com- 

 plicated structure. The eggs appear to be extruded in a string of 

 tough gelatinous material which becomes surrounded by the matrix 

 jelly forming the body of the ribbon. The string itself is laid in 

 a zigzag fashion, so that the appearance is that of a double row 

 of eggs. It is, however, accurately placed in the form of a flat- 

 tened spiral so that the loops are not formed by simple back and 

 forth folds as they at first appear, but are so arranged that the 

 loops are compressed against each other. This produced the effect 

 of a thick cross-striated ribbon. In one typical ribbon 242 loops 

 were counted, in each of which the eggs averaged 90; this gave a 

 total of 21,780 eggs for this ribbon. Probably 20,000 is an aver- 

 age number for a ribbon produced under typical conditions. 



In each ribbon the eggs are uniformly all in the same stage of 

 development, indeed in the same stage of mitotic division. It is 

 a remarkable fact that 20,000 eggs should be deposited in as com- 

 plicated a manner as these and all be in the same stage of division. 

 But it is this fact in connection with the ribbon-like egg case that 

 renders them desirable for experimental purposes. In conducting 

 the experiments a ribbon would be cut into segments, one or more 

 of which would form a control, while the others would be placed 

 in the various solutions as desired and the results noted in com- 

 parison to the control. 



The purpose of the first experiments upon these eggs was to 

 verify and to extend Loeb's observations on Arbacia eggs that a 

 small amount (.006 per cent.) of sodium hydrate would accelerate 

 development. A considerable number of experiments planned to 

 determine the effect of various concentrations of NaOH on the 

 eggs were carried on. The general results of these were two. 

 Some acceleration of cleavage resulted if the eggs were allowed to 

 develop in sea water containing from .004 per cent, to .009 per 

 cent. N'aOH. Acceleration of cleavage does not always result in 

 an earlier hatching of the larvse, for it would seem that the advan- 



