378 FRANK R. LILLIE 
probably is that a sperm nucleus may persist to a certain 
extent even if injured and unable to produce the full fertilizing 
effect and cause cleavage. 
A third reason for discrepancy in the results is that abnorm- 
alities of maturation may be produced by centrifuging which 
render the determination of the sperm nucleus more difficult 
than usual. It frequently happens that, as the first matura- 
tion spindle is driven from the surface by the centrifugal force, 
it divides before it reaches the surface again, producing two 
maturation nuclei within the egg. The two second maturation 
spindles may then unite to form a tetraster, one pole of which 
approaches the surface and a single polar body is formed, leaving 
three nuclei within the eggs (fig. 7). Such eggs were readily 
recognized by the absence of the first polar globule, and by the 
presence of the extra nuclei. But it was sometimes difficult to 
determine in certain stages whether there were only three nuclei, 
the sperm nucleus being absent, or four, the sperm nucleus being 
present. 
A fourth reason for a certain discrepancy between the esti- 
mate of the number of eggs that segmented and the number 
determined to have sperm nuclei might be that at the time the 
experiment was made the importance of exact determination of 
the number of eggs that segmented was not realized, and the 
determination was made only roughly. Putting the results 
side by side we have: 
PERCENTAGE OF EGGS PERCENTAGE DETERMINED 
OBSERVED TO DIVIDE BY SERIAL SECTIONS TO 
IN LIVING CONDITION | POSSESS SPERM NUCLEI 
27 Controle st Se eres | All All 
BIN. «5. ses RS eae ee | About 20 per cent About 37 per cent 
id SEER Soh Pd A CR a | 5 to 10 per cent About 10-20 per cent 
“yt ORME Lo Bee) Sea About 20 per cent About 25 per cent 
PUD Ae OAR sn SB Ce | About 50-60 per cent About 53 per cent 
Di eee ane. ea About 75-90 per cent About 76 per cent 
Considering the various sources of error, the agreement is 
very close except in 27A. But in this case we do not have to 
