The relationship between cleavage and blastocoel formation in Xenopus laevis

The development of the blastocoel in Xenopus laevis was studied by electron microscopy. Two major morphological specializations were associated both with blastocoel formation and with cleavage. The first specialization was the formation of close junctions at specific points along cleavage furrows, starting as early as the first division. The second was the secretion of material into the blastocoel and extracellular spaces. Secretion occurred by three processes, one merocrine, the other two apocrine. The main secretory product released was /?-glycogen, although other products were also liberated. The membrane added to the cell surface during secretion contributed to the growth of both the blastocoel and the furrows. Filaments 80 A in diameter were found to be present at some, but not all, furrow tips during embryogenesis, but the filaments apparently played no direct role in the formation of the blastocoel.