374 “FRANK R. LILLIE 
ent eggs. The extreme viscidity of the jelly gradually dis- 
appears, and after about twenty minutes from insemination, the 
eggs no longer mat together. It is therefore difficult to investi- 
gate the effects of centrifuging on the developmental capacity 
of the eggs during the first ten or fifteen minutes after insemin- 
ation. However, when the viscid stage begins to pass away 
and eggs can be separated from the mass for examination, the 
majority are found to undergo segmentation, as many as 98 per 
IO 20 30 40 50 60 70 
Fig. C. The effectsof centrifuging on the power tosegment in Nereis. The ab- 
scissae represent minutes from the time of i semination, the ordinates the percen- 
tage of eggs dividing. At position a penetration of the spermatozoon is just 
completed in most of the eggs. At position b the first polar body is extruded. 
Data from experiment 2, 1910. 
cent in one case (experiment 2, fos) twenty-one minutes after 
insemination. 
3. For about the next thirty minutes (twenty-one to fifty- 
three minutes after insemination) centrifuging tends to inhibit 
the cleavage of a certain proportion of the eggs which gradually 
increases up to about thirty-seven minutes after insemination 
and then decreases again. For instance, in experiment 2 of 
1910, of the eggs centrifuged twenty-one minutes after insemin- 
ation 98 per cent segmented; twenty-six minutes after insemin- 
ation 36 per cent segmented; thirty-two minutes, 33 per cent; 
thirty-seven minutes, 21 per cent segmented; forty-three min- 
utes, 26 per cent segmented; forty-eight minutes, 52 per cent 
segmented; fifty-three minutes, 75 per cent segmented; fifty- 
