The newly spawned amphioxus <i>B. belcheri</i> and their sections.

<p>Animal A is a typical Category II animal, animal B is a typical Category I animal, and animal C is Category I animal one day post spawning. Vertical lines in the photos at the top line (a–f) indicate where the sections in the middle line (g–l) were performed and the figures (m–r) shown at the bottom are higher magnifications of the regions highlighted by black boxes on the sections in the middle. The gonads in the figures at the bottom are highlighted with blue dotted lines. Arrows in m indicate the unspawned ripe eggs of Female A; arrow in n indicates the thin germinal epithelium (with few spermatocytes inside) of Male A; arrows in o indicate the unreleased immature small oocytes (5–50 micrometer in diameter) of Female B; arrow in p shows many unspawned spermatocytes of Male B; arrows in q indicate the redeveloping oocytes of Female C; and arrow in r indicates redeveloping spermatocytes of Male C.