Fertilization currents are similar in ascidian oocytes and fragments, irrespective of the size and global origin of the fragments; this result suggests that fertilization channels are distributed uniformly over the oocyte surface. Because no correlation exists between peak current and surface area of the cell, it is probable that the fertilizing spermatozoon does not open all available precursor fertilization channels, but a fixed number limited to an area around its point of entry.