Rat Development Stages
From Embryology
Witschi Rat Stages
Shown below are the Witschi standard stages of development[1] and the timing and specific features that identify each stage. See also the Rat Timeline which gives a day by day sequence and adds additional research findings on rat development.
| 1 | 1 | 0.07 | 1 cell (in oviduct) |
| 2 | 2 | 0.08 x 0.06 | 2 cells (in oviduct) |
| 3 | 3 | 0.08 x 0.05 | 4 cells (in oviduct) |
| 4 | 3.25 | 8-12 cells (in oviduct) | |
| 5 | 3.5 | 0.08 x 0.04 | Morula (in uterus) |
| 6 | 4 | (0.08 x 0.03) | Early blastocyst (in uterus) |
| 7 | 5 | (0.12 x 0.05) | Free blastocyst (in uterus) |
| 8 | 6 | (0.28 x 0.07) | Implanting blastocyst, with trophoblastic cone and inner cell mass; outgrowth of endoderm (hypoblast) |
| 9 | 6.75 | Diplotrophoblast; inner cell mass (pendant), covered with endoderm | |
| 10 | 7.25 | (0.3 x 0.1) | Near complete implantation; pendant begins differentiation into embryonic and extra-embryonic parts |
| 11 | 7.75 | (0.5 x 0.1) | Completion of implantation; primary amniotic cyst; ectoplacental cone |
| 12 | 8.5 | (1.04 x 0.26) | Connecting ectochorionic and amniotic cavities; rudiments of amniotic folds; primitive streak; start of 3rd layer formation; blastemas of heart and pericardium |
| 13 | 9 | 1.0 | Presomite neurula; fusion of chorio-amniotic folds, chorio-amniotic stalk; neural plate; embryo bent dorsally; bud of allantoic stalk |
| 14 | 9.5 | 1.5 | Somites 1-4 (occipital); pendant with 3 cavities: ectochorionic cyst, exocoelom, and amniotic cavity; ectochorionic cyst collapsing; allantoic stalk projects into exocoelom; embryo bent dorsally |
| 15 | 10 | 2 | Somites 5-12 (cervical); 1st visceral arch; ectochorionic cyst fused with ectoplacenta and with allantoic stalk; regression of peripheral (distal) yolk sac and trophectoderm (diplotrophoblast); Reichert's membrane; gonia in endoderm; embryo bent dorsally |
| 16 | 10.5 | 2.4 | Somites 13-20 (upper thoracic); 2 visceral arches; disc and yolk sac placentas; appendicular folds; embryo reverses, curves ventrally |
| 17 | 11 | 3.3 | Somites 21-25 (lower thoracic); yolk stalk closes at level of 15th somite; primary gonia in mesentery; primitive streak disappears; tail bud becomes organized; arm and leg buds recognizable |
| 18 | 11.5 | 3.8 | Somites 26-28 (upper lumbar); 3 visceral arches; arm buds recognizable |
| 19 | 11.75 | 4.2 | Somites 29-31 (lower lumbar); visceral arches I-IV; cervical folds; appendicular folds and buds |
| 20 | 11.875 | 5 | Somites 32-33 (upper sacral) |
| 21 | 12 | 5.1 | Somites 34-35 (lower sacral); deep cervical sinuses |
| 22 | 12.125 | 5.2 | Somite 36 (1st caudal); olfactory pits |
| 23 | 12.25 | 5.6 | Somites 37-38 (caudal); start of umbilical herniation |
| 24 | 12.375 | 6 | Somites 39-40 (caudal) |
| 25 | 12.5 | 6.2 | Somites 41-42 (caudal); occipital somites dispersing; 4 visceral arches; deep cervical sinuses; arm buds at somite levels 8-14, about as high as long; leg buds at somite levels 28-31, smaller; body forms a spiral of about 11/2 turns, the left face and trunk applied to yolk sac, the right side turned toward placenta; tail and allantoic stalk rise to the placenta |
| 26 | 12.75 | 7 | Somites 43-45 (caudal); mandibular, maxillary, and frontonasal processes; cervical sinuses closing; mammary welts; differentiaion of handplates; arm buds vascularized, brachial nerves entering; beginning of umbilical hernia |
| 27 | 13 | 8 | Somites 46-48 (caudal); prominent facial processes and clefts; nose-snout projecting; cervical sinuses closed; primordia of mammary glands; round handplates and footplates; larger umbilical hernia |
| 28 | 13.5 | 8.5 | Somites 49-51 (caudal); 1st visceral cleft transforms into external ear duct; precartilaginous condensations in handplates |
| 29 | 14 | 9.5 | Somites 52-55 (caudal); auricular hillocks on visceral arches I and II |
| 30 | 14.5 | 10.5 | Somites 56-60 (caudal); body uncoils; mandibular precartilage; nearly round opening of external ear duct; pleuroperitoneal canal has become very narrow |
| 31 | 15 | 12 | Somites 61-63 (caudal); facial clefts closed; pleuroperitoneal canal closed; complete diaphragm |
| 32 | 15.5 | 14.2 | Somite 64 (caudal); pinna turns forward; maximal size of umbilical hernia |
| 33 | 16 | 15.5 | Somite 65 (usually this is last caudal); snout lifts off chest; last stage of metamorphosis |
| 34 | 17-18 | 16-20
|
1st fetal stage: rapid growth of eyelids (eyes entirely covered at end of 18th day); palate complete; pinna covers ear duct; umbilical hernia withdraws |
| 35
ante-natal |
19-22 | 20-40
|
2nd fetal stage: sealed eyelids; fetal membranes and placentas reach peak of development; tail grows to 10mm;
Birth occurs (22nd day in rat, 19th day in mouse) |
| 35
post-natal |
1-16 post-partum | 40-1001 | After birth, fetus becomes a breathing and suckling nestling2; during 1st 16 days (22 to 38 days total age), eyelids remain sealed and external ear ducts plugged with periderm |
| 36
post-natal |
17+ post-partum | 100+1 | Periderm seals of ears and eyelids vanish; active feeding begins within next 3 days and weaning after 1 week (total weaning age, 45-48 days for rats and mice) |
| Reference: Witschi E. Rat Development. In: Growth Including Reproduction and Morphological Development. (1962) Altman PL. and Dittmer DS. ed. Fed. Am. Soc. Exp. Biol., Washington DC, pp. 304-314. Lnks: rat
| |||
Somite Timeline
| Maximum Variation | |||||||
|---|---|---|---|---|---|---|---|
| Age Days-Hrs. |
Number of Litters |
Number of Embryos Counted |
Means | All Embryos | One Litter | Standard Deviation |
Coefficient of Variation % |
| 10-12 | 1 | 4 | 8.7 | 6-11 | 6-11 | 2.8 | 32 |
| 10-13 | 1 | 6 1 | 0. 2 | 8-13 | 8-13 | 1.9 | 19 |
| 10-16 | 2 | 12 | 12.4 | 6-26 | 6-26 | 5.8 | 47 |
| 10-17 | 6 | 48 | 12.9 | 4-26 | 7-26 | 3 .3 | 26 |
| 10-18 | 4 | 23 | 14.1 | 6-18 | 9-18 | 3.1 | 22 |
| 10-19 | 1 | 6 | 14 .3 | 12-17 | 12-17 | 1.2 | 8 |
| 10-22 | 3 | 16 | 13.1 | 6-19 | 6-14 | 3.9 | 30 |
| 10-23 | 3 | 17 | 15.2 | 8-18 | 8-18 | 2.4 | 16 |
| 11-00 | 2 | 0 | 14.6 | 10-17 | 10-17 | 1.9 | 13 |
| 11-02 | 2 | 15 | 20 . 9 | 17-22 | 17-22 | 1. 3 | 6 |
| 11-04 | 1 | 10 | 25. 3 | 23-26 | 23-26 | 1.2 | 5 |
| 11-06 | 1 | 2 | 18.0 | 18-18 | 18-18 | .0 | 0 |
| 11-08 | 1 | 8 | 25 0 | 23-28 | 23-28 | 1.9 | 8 |
| 11-09 | 1 | 3 | 22 .0 | 20-25 | 20-25 | 2 . 2 | 10 |
| 11-10 | 2 | 18 | 26.2 | 21-31 | 21-31 | 2.9 | 11 |
| 11-11 | 3 | 26 | 25.6 | 14-29 | 14-27 | 3.2 | 12 |
| 11-12 | 1 | 3 | 26. 7 | 25-28 | 25-28 | 1.2 | 4 |
| 11-14 | 1 | 3 | 21.3 | 21-22 | 21-22 | .6 | 2 |
| 11-15 | 1 | 8 | 23.1 | 17-28 | 17-28 | 4 . 0 | 17 |
| 11-16 | 1 | 7 | 26.7 | 24-28 | 24-28 | 1.3 | 5 |
| 11-17 | 1 | 7 | 26.1 | 25-28 | 25-28 | 1.1 | 4 |
| 11-18 | 3 | 25 | 25 .4 | 19-28 | 19-28 | 1.9 | 7 |
| 11-20 | 2 | 16 | 27.2 | 25-29 | 25-29 | 1.2 | 4 |
| 23 Ages | 44 | 292 | Av 2.2 | Av 13% | |||
| Data Reference[2] Links: rat | somitogenesis | |||||||
Species Stages Comparison
The table below gives an approximate comparison of human, mouse and rat embryos based upon Carnegie staging.
| Carnegie | Stage | |||||||||||||||||||||||
| Human | Days | 1 | 2-3 | 4-5 | 5-6 | 7-12 | 13-15 | 15-17 | 17-19 | 20 | 22 | 24 | 28 | 30 | 33 | 36 | 40 | 42 | 44 | 48 | 52 | 54 | 55 | 58 |
| Mouse | Days | 1 | 2 | 3 | E4.5 | E5.0 | E6.0 | E7.0 | E8.0 | E9.0 | E9.5 | E10 | E10.5 | E11 | E11.5 | E12 | E12.5 | E13 | E13.5 | E14 | E14.5 | E15 | E15.5 | E16 |
| Rat | Days | 1 | 3.5 | 4-5 | 5 | 6 | 7.5 | 8.5 | 9 | 10.5 | 11 | 11.5 | 12 | 12.5 | 13 | 13.5 | 14 | 14.5 | 15 | 15.5 | 16 | 16.5 | 17 | 17.5 |
| Note these Carnegie stages are only approximate day timings for average of embryos. Links: Carnegie Stage Comparison | ||||||||||||||||||||||||
| ||||||||||||||||||||||||
References
- ↑ Witschi E. Rat Development. In: Growth Including Reproduction and Morphological Development. (1962) Altman PL. and Dittmer DS. ed. Fed. Am. Soc. Exp. Biol., Washington DC, pp. 304-314.
- ↑ Landacre FL. and Amstutz MM. Data on the number of somites compared with age in the white rat. (1929) Ohio J. Science. 29(6): 253-259.
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Cite this page: Hill, M.A. (2026, March 7) Embryology Rat Development Stages. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Rat_Development_Stages
- © Dr Mark Hill 2026, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
