Pederin (10−4M and 2.10−4″M), acting on the cleaving eggs ofTriturus helveticusRaz., does not prevent or arrest cleavage before mitosis. It dissociates the achromatic apparatus from the nuclei, inducing achromosomic mitoses, but does not destroy either the spindle or the asters. Disfunction of kinetochores results in aberrant polar chromosomes not being included in the equatorial plate (so-called three groups metaphase) and aberrant caryomeres.