Lab., Woods Hole 183, 258-268), few larvae started gastrulation after 30 hours. Although cells in the alkaline-phosphatase-positive area 2 are added to the posterior end of the archenteron after 30 hours in normal development (R. However, when the volume deleted was less than 6%, most of the larvae started archenteron formation before the intact controls reached the mesenchyme-migration stage (30 hours). When the vegetal oocyte fragment, the volume of which was more than 8% of that of the whole oocyte, was removed from the immature oocyte, archenteron formation was strongly suppressed. Alkaline-phosphatase-positive area 2, which was gradually added to the posterior end of the archenteron after 30 hours, became alkaline-phosphatase-positive and formed the middle-to- posterior part of the stomach and the intestine. The alkaline-phosphatase-positive area 1 gave rise to the esophagus and the anterior end of the stomach. The anterior negative area differentiated into mesodermal tissues such as mesenchyme cells and anterior coelomic pouches (anterior mesodermal area). At 27 hours after 1-methyladenine treatment, the whole archenteron except the anterior end started to express alkaline phosphatase.

The archenteron (and the differentiated digestive tract) of Asterina pectinifera was divided into three areas based on the time of start of alkaline phosphatase expression. Contribution of maternal cytoplasmic factors and cellular interaction to determination of archenteron in a starfish embryo was analyzed by (1) examining temporal and positional pattern of expression of an endoderm-specific enzyme, alkaline phosphatase, (2) deleting the vegetal polar fragment from an immature oocyte and (3) changing the orientation of a blastomere within an early stage embryo.

Asterias blastopore