Fig. 10

25-h larva. a DIC of living 25-h larva with recently opened mouth (arrow). Scale bar = 100 μm. b Enlargement of anterior end of a; asterisk and arrow indicate, respectively, Hatschek’s left diverticulum and mouth. The rhombus indicates the rombohedral volume where SBSEM series were reconstructed in 3-D in c–e. Scale bar = 50 μm. c Left side view of a 3-D reconstruction. The ectoderm is not shown. The arrowhead points to the external opening of the club-shaped gland; α and β indicate, respectively, the oblique planes of the SBSEM scans in Fig. 11a, b. Scale bar = 50 μm. d Same reconstruction as d, but showing the notochord and the semitransparent ectoderm, which is discontinuous over Hatschek’s left diverticulum (asterisk), opening of the club-shaped gland (arrowhead), and mouth (mo); the last is encircled by oral mesoderm cells (depicted in various colors). Scale bar = 50 μm. e Reconstruction like d, but turned to show left-side structures from a medio-posterior viewpoint. Scale bar = 50 μm. f enlargement of the oral region of e, with the subendodermal basal lamina indicated by parallel black traces. Scale bar = 20 μm. ect, ectoderm; fls, first left somite; fmp, flagellar/microvillar process; Hld, Hatschek’s left diverticulum; Hn, Hatschek’s nephridium; Hrd, Hatschek’s right diverticulum (often termed the rostral coelom by this stage of development); lpm, lateral plate mesoderm; mo, mouth; no, notochord; pe, pharyngeal endoderm; pl, pharyngeal lumen; om, oral mesoderm; sls, second left somite