TEMPORAL RELATIONS BETWEEN EXTENSION OF ARCHENTERON ROOF AND REALIZATION OF NEURAL INDUCTION DURING GASTRULATION OF NEWT EMBRYO

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Abstract
This investigation was performed in order to analyze the basic relationships between the archenteron roof and the overlying ectoderm in primary induction in the Cynopus (Triturus) pyrrhogaster embryo. The part of the archenteron roof that is active in inducing capacity extends linearly after invagination at the speed of 0.15 mm per hr at 23°C until stage 13b. The period of contact at each position of the presumptive neuro-ectoderm with the active archenteron roof could be estimated by the formula described in the Discussion. Pieces of the presumptive neuro-ectoderm were isolated from gastrulae at three developmental stages and cultured separately in Holtfreter solution after being divided caudo-cranially into 4 parts. The result showed that some of them were able to differentiate into neural tissues even in the mid-gastrula stage and that the presumptive neuro-ectoderm acquired the capacity to differentiate into neural tissue along a caudocranial axis from the part adjacent to the blastopore during gastrulation. It could be estimated that 3 hr of contact with the active archenteron roof is sufficient for the presumptive neuro-ectoderm to differentiate into neural tissue. The present study also showed that the neuralizing capacity of the whole prospective neuro-ectodermal area has already been determined before the end of stage 13, i.e., within less than 14 hr after first contact of the ectoderm with the active archenteron roof at 23°C.