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Summary
The regeneration of the digestive system in 5-month-old pentactulae of the holothurian Eupentacta fraudatrix was examined using light and transmission electron microscopy. Transversely bisected pentactulae are devoid of posterior intestinal parts and a rectum. The regeneration of the intestine proceeds at the expense of the tissues of the gut remnant. The most important morphogenetic events are proliferation of the differentiated cells in the lining epithelium, and dedifferentiation followed by mitotic division, migration and redifferentiation in the mesothelium. The dividing cells are scattered randomly and no blastema is formed. Both dividing and migrating cells retain their intercellular junctions. The rectal rudiment appears as an epidermal invagination. Both intestinal and rectal rudiments move toward each other before merging. A hypothesis is advanced that the pattern of gut regeneration in the pentactulae of E. fraudatrix is a recapitulation of the ancestral mechanism of gut regeneration in holothurians.
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