Template:Axolotl timeline

From Embryology
Axolotl Timeline
Stage Time (hours) Description
1 0 Freshly laid egg in jellycoat.
2 First appearance of the first cleavage furrow and the animal pole.
3 2.5 Four cells.
4 4 Eight cells.
5-6 5.5 16 cells.
6 6.5 - 7 32 cells
7 8 - 9 64 cells
8 16 Early blastula (fall of mitotic index in animal blastomeres).
9 21 Late blastula, surface is smooth.
10 26 Early gastrula I, first sign of dorsal blastopore lip.
11 38 Middle gastrula II, Blastopore covers three quadrants. Lateral lips are formed; ventral lip is marked only by pigment accumulation. Yolk plug reaches its maximum diameter.
12 47 Late gastrula II, Blastopore has an oval or circular shape.
14 58 Early neurula II: Neural plate is broad. Neural folds are outlined and begin to rise above the surface in the head region. Embryo is slightly elongated.
15-16 59 - 63 Early neurula III and middle neurula: Neural plate is shield-shaped and becomes sunken; neural folds are raised and bound all regions of the neural plate.
17 64 Late Neurula I: Neural folds are higher; especially in the head region. Further narrowing and deepening of the neural plate occur both in the head and in the spinal regions. Hyomandibular furrow limiting the mandibular arch is slightly outlined. The segmentation of the mesodermal material begins. There are two pairs of somites.
18 66 Late neurula II: Neural plate is deeply sunken. Neural folds are closing and are especially high in the head region where three slight bulges corresponding to fore-, mid- and hindbrain vesicles are outlined. The neural folds of the spinal region are almost in contact. Hyomandibular furrow is more marked. There are two pairs of somites.
19 69 Late neurula III: Neural folds are in contact throughout, but are not yet fused. Brain curvature is quite distinct in profile; fore-, mid- and hindbrain vesicles are also distinct. The swelling of optic vesicles is outlined (barely visible in these pictures because of unfortunate perspective). Hymandibular furrows are deeper. There are three pairs of somites.
20 70 Late Neurula IV: Späte Neurulation IV: Neural folds are fused in spinal region (or are starting this process in these pictures); in brain region, they are only in contact. Optical vesicles are destinct and becoming larger. Grooves in ectoderm appear at the level of the hindbrain. A very slight swelling marks the future gill region. Mandibular arch becomes prominent and four pairs of somites are present.
22-23 73-74 Neural folds are completely fused. The gill region and the pronephros are distinct; the tailbud is slightly outlined. Five to six pairs of somites are present. Primordium of the ear is outlined as a shallow depression in the ectoderm in the region above the future hyoid arch. The hyobranchial furrow appears, outlining the boundary between the hyoid arch and the first branchial arch.
24 80 Ear pit is outlined and becomes more distinct. The hyobranchial furrow lengthens ventrally. The prophenic swelling is clearly outlined, and both the pronephros itself and the beginning of the pronephric duct are clearly visible Eight or nine pairs of somites are visible.
29 Since first cleavage, up to 97 hours have passed (sorry, I missed some hours here... ;-) ). Ear pit becomes quite distinct. The gill region is clearly outlined. The pronephric duct is clearly visible along six somites at least. The primordium of the olfactory organ appears as a tubercle on the anterior part of the head; the tailbud is gradually enlarging in all stages. Up to 16 pairs of somites are present.
30-31 110 The body of the embryo continues to straighten; the tailbud enlarges. Dorsal finfold begins at somite 14-12. A groove appears in the region of the lens primordium (visual system - i.e. eyes) The third branchial furrow becomes apparent in the dorsal part of the gill region.
32-34 115 The dorsal fin develops until it begins at somite 10.
35 122 From this stage on, the body axis from the hindbrain to the tail base are quite straight. Three external gills show ad nodules on the surface of the gill swelling. The lateral line reaches to the sixth somite. The dorsal fin begins at the fifth somite. The first chromatophores appear; heart pulsation begins.
36-37 177 Gills elongate and push venventroposteriorly. No limb buds are yet visible.
38 Filament sprouts appear as two nodules on each gill. The primordium of the operculum is visible as a fold upon the hyoid arch. Neither of the two rudiments of the perculum reaches the midline. The limb buds are slightly outlined.
39 220 The first gills have two pairs of filament sprouts; the second and third have three pairs each. The gills cover the limb buds. Both rudiments of the operculum approach the midline. The angle of the mouth begins to show.
40 240 The gills are longer and the number of filaments increases (four pairs in the first gills, six or seven pairs on the second or third gills). The rudiments of the operculum join at the middline. The angles of the mouth are marked more distinctly and limb buds protrude slightly.
41 265 The gills contunie to elongate, the number of filaments increases and they become longer. The mouth is distinctly outlined. The second lateral line runs along the flank toward the limb bud and bypasses it on the ventral side. Hatching begins.
42 296 The gills extend far beyond the forelimb buds. The mouth is completely outlined, but is not broken through.
43 With galvanic and convulsive movements the larva breaks free of the jelly coat. The mouth either is already opened or will open within the next 24 - 72 hours.
  1. Bordzilovskaya NP, Dettlaf TA, Duhan ST, Malacinski GM: Developmental-stage series of axolotl embryos. In Developmental Biology of the Axolotl. Edited by: Armstrong JB, Malacinski GM. New York: Oxford University Press; 1989:201-219.