MORTALITY IN PIKE-PERCH EGGS IN HATCHERIES. 3 
therefore, comes on that part of the protoplasmic investment of the yoke which 
covers the oil globule and here it bursts. In almost every case the white spot 
which indicates the rupture of the yoke investment makes its appearance at 
the oil globule, usually at the equator. 
Almy’s as well as our own observations show that the death rate 
increases rapidly and steadily to the fourth day and then advances 
more slowly. To begin with, it must be noticed that a small per- 
centage of dead eggs is found practically as soon as the fishes are 
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Age of eggs in hours. 
Fic. 1.—Graph showing the variation in numbers of abnormal and unsegmented pike- 
perch eggs during development. 
stripped. It is surmised that these may have been injured in the 
process of stripping, or that they may have died through some de- 
velopmental irregularity while still in the fish. 
Coming now to the hypothesis that failure of fertilization is re- 
sponsible for a greater part of the mortality of hatching eggs, it is 
generally assumed that lack of impregnation and failure to segment 
are closely correlated. A detailed examination of the material does 
not bear this out. We found that in eggs 4 hours 30 minutes old there 
was a considerable percentage which showed no trace of cleavage. 
This was true also at 5 hours 30 minutes, 6 hours 45 minutes, and 
