Studies of mitosis in excised limb regenerates of the newt, Notophthalmus viridescens.

Subsequent to excision and explantation of the limb blastema into culture medium, there is an abrupt reduction in mitotic index lasting several hours. Coincident with the disappearance of mitosis, abnormal mitotic figures (AMFs), lacking the condensed chromosomal nature of normal figures, are seen. These persist until normal levels of mitotic activity are restored approximately 6 hr later. The transient loss of mitotic activity is observed in both ganglionated and nonganglionated explants. The large number of prophase figures observed at time zero were sharply reduced within minutes, without concomitant increases in the later phases. The possibility that some cells, without completing mitosis, become temporarily indistinguishable as mitotic figures, is discussed in terms of chromosomal decondensation and recondensation.