Influence of the antimitotic naphthoquinone on the cleavage of the eggs of the mollusc,Mytilus edulis L.

1. A brief account is given of the cleavage ofMytilus edulis L.2.Naphthoquinone in concentrations above 1∶ million produces cytolysis of the newly fertilised eggs. It causes some blockage of cleavage at the single cell stage in concentrations down to 1∶40 M. The main area of its antimitotic activity is in the range between 1∶ M and 1∶6 M. Resistance to the substance increases as cleavage proceeds. 3. Some abnormalities of cleavage are found at all antimitotic concentrations. The types of abnormality are described. They do not appear to fit easily into the hypothesis of Huber (1947) that the effect of this substance is to enhance the contraction and inhibit the expansion of the cell cortex.