226 E. E. JUST 
According to Schaxel, the middle-piece does not enter the egg 
of echinoderms. Meves will not admit this for echinids and 
doubts that in Nereis the middle-piece is left outside the egg 
while denying the centrosome the chief part in fertilization. 
In Platynereis, as in Nereis, by diverse methods it can be shown 
that the middle-piece does not enter the egg. We are thus 
forced to conclude that, whatever its rdle, the middle piece in 
Platynereis can play no part, either in heredity or through a 
centrosome in the dynamics of fertilization. 
Marine Biological Laboratory Woods Hole, Mass. 
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