Intranuclear Annulate Lamellae in Ascidian Embryos

Adult Boltenia villosa (phylum, Chordata; subphylum, Urochorda [Tunicata]; class, Ascidiacea) were collected intertidally. Gametes and embryos were handled according to standard procedures (Fernald, 1959; Costello et al., 1957). Living embryos in gastrula or neurula stages were pipetted into the fixative accompanied by a small amount of seawater. The fixative was either (a) 2.7% Os04 in approximately 0.2 M bicarbonate buffer, or (b) 2% Os04 in 0.1 M phosphate buffer. After fixation for 2 hr at 0-4 C, the specimens were rapidly dehydrated in a graded ethanol series, left for 30 min in absolute ethanol, and embedded in Epon (Luft, 1961). Thin sections were stained with lead tartrate (Millonig, 1961) and examined in an RCA 2A electron microscope.