EXPERIMENTS ON THE NORMAL MEIOTIC BLOCK IN THE OVUM OF TRITURUS VIRIDESCENS

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Abstract
In Triturus viridescens the first meiotic spindle forms at about the time the egg leaves the ovary, and the first division is usually completed as the egg passes through the anterior parts of the oviduct. The second division figure then forms, but the division is usually arrested at metaphase until fertilization occurs. Oviducts were ligated at several levels to retain oocytes from 48 to 72 hours in the coelom or in certain regions of the oviducts. Advances past metaphase II occurred in these oocytes, but at a low frequency, and were confined to eggs never exposed to the jelly secreted by the oviducts. Twenty-two per cent of the eggs (non-jelly-covered) removed from the coelom or ostium of the oviduct and kept in vitro (usually for 24 hours) advanced past metaphase n, but eggs with oviducal jelly did not advance. Only one doubtful advance was observed in eggs from which the jelly had been mechanically removed prior to their stay in vitro. Some of the "advanced" eggs exhibited post-meiotic "mitotic" activity. The jelly secreted by the oviducts is of significance with regard to meiotic arrest under the conditions of these experiments, and may play some role in normal arrest, but the evidence does not allow a decision as to the source of the arrest.