The Ultrastructure of Brood Pouch Formation in Tokophrya infusionum

SYNOPSIS Asexual reproduction in Tokophrya infusionum is by internal budding, whereby a ciliated, motile embryo is formed inside the sessile, non-ciliated parent in a specialized structure, the brood pouch. The process of embryogenesis and brood pouch formation was studied with the electron microscope using synchronized cultures. Reproduction begins with invagination of the pellicle and plasma membrane in the apical region of the adult. Early invagination is characterized by the presence of numerous microtubules beneath the plasma membrane or epiplasmic layer of the invaginating membranes. These microtubules apparently are important in formation of the brood pouch for colchicine blocks embryogenesis during the early stages. When the embryo is completed, it is ejected from the brood pouch thru the birth pore, an opening which is the site of the initial invagination and is present thruout embryogenesis. Theories of brood pouch formation are reviewed and discussed in light of the present investigation.