Abstract
The cell cycle in the overgrown optic tectum of the chick embryo was investigated radioautographically from the 3rd through the 6th day of incubation. Quantitative data were obtained on the length of the DNA-synthetic period (S), the premitotic period (G 2), mitosis, and the postmitotic period (G 1). At each stage of development, the total generation time in the abnormal brain showed an increase of approximately 2–3 h over that observed in the normal brain. The duration of mitosis, G 1, and the S period likewise increased. The results indicate that although one sees an increased number of mitotic figures during overgrowth, this may reflect a longer period of time spent in mitosis, rather than an actual increase in proliferative activity. This suggests that the term ‘overgrowth’ is a misnomer for a condition which actually involves a slowing down of the proliferative process.
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