Fine structure of the sperm storage tubules in the box turtle oviduct.

The sperm storage tubules of the box turtle (Terrapene carolina) were examined by transmission electron microscopy. Tubules containing spermatozoa were surrounded by 6-8 secretory cells, each of which contains numerous membrane-bound vesicles presumably containing precursors to egg white proteins. The apical membranes of these cells contain microvilli, and the apical lateral membranes possess prominent junctional complexes. Cells comprising the spermatozoa-containing tubules cannot be differentiated from those devoid of spermatozoa. Various quantities of spermatozoa reside free in the lumina of the secretory tubules, and are not in contact with host cells. Only the presence of ducts communicating with the oviduct lumen serve to differentiate the spermatozoa-containing tubules.