OTTO GLASER. 

 IV. ANALYSIS BY MEANS OF THE RATE OF CLEAVAGE. 



A. THE EFFECT OF EGG-SECRETION IN NORMAL AND ALKALINE 



SEA-WATER. 



A first step toward an answer however has been taken in the 

 form of experiments in which known quantities of egg-secretion 

 were added to normally fertilized eggs and the rate of cleavage 

 compared with controls. The secretions used in these experi- 

 ments were standard, prepared as before. 



Many notes were taken in making these comparisons for it 

 could not be foreseen which details might be utilized as indicators 

 of the relative rates of development. Of all these however only 

 certain data with respect to the 2, 4, and 8-cell stages are reported. 

 This choice depends entirely on the advantage of reporting the 

 more easily verifiable facts, and not because other details are 

 in any way contradictory. Indeed the reverse is true and applies 

 to such stages of the division spindles as can be clearly recognized 

 in the living egg. Similar conclusions also can be drawn from 

 the later stages, although it is much more difficult to tell at a 

 glance whether a certain culture of blastulse, gastrulse or plutei, 

 is more or less advanced than a given standard. I wish to 

 emphasize the fact however that these later stages were obtained 

 in large yields in the experimental cultures and were normal, 

 though often somewhat slower of movement. 



Several ways of comparing the rates of cleavage are open. 

 Of these the following two were adopted: the time (minimum, 

 in the table) that elapsed between insemination and the first 

 2, 4, or 8-cell stage seen in a particular culture is given, as well 

 as the interval (maximum, in the table), between insemination 

 and the time at which the cultures were at the height of these 

 respective stages. The results of the second way of counting are 

 in the same sense as the others, but are less accurate since there 

 is greater opportunity for errors of judgment, whereas no error 

 of judgment is likely with respect to the recognition of the first 

 2, 4, or 8-cell stage seen. The possibility that the particular 

 cases observed were not the first to appear in the cultures of 

 course remains, but a moment's examination of Table I will show 

 that with very considerable errors of this sort consistent results 

 could hardly have been obtained. 



