Rat Timeline

Rat Development

rat

Day 1

Standard Witschi Stage 1, day 1 , Size (mm)0.07
Features: Cleavage and Blastula, 1 cell (in oviduct)

Day 2

Standard Witschi Stage 2, day 2 , Size (mm)0.08 x 0.06
Features: Cleavage and Blastula, 2 cells (in oviduct)

Day 3

Standard Witschi Stage 3, day 3 , Size (mm)0.08 x 0.05
Features: Cleavage and Blastula, 4 cells (in oviduct)

Standard Witschi Stage 4, day 3.5
Features: Cleavage and Blastula, 8-12 cells (in oviduct)

Standard Witschi Stage 5, day 3.25 , Size (mm)0.08 x 0.04
Features: Cleavage and Blastula, Morula (in uterus)

Day 4

Standard Witschi Stage 6, day 4 , Size (mm) (0.08 x 0.03)
Features: Cleavage and Blastula, Early blastocyst (in uterus)

Day 5

Standard Witschi Stage 7, days 5 , Size (mm) (0.12 x 0.05)
Features: Cleavage and Blastula, Free blastocyst (in uterus)

Day 6

Standard Witschi Stage 8, days 6 , Size (mm) (0.28 x 0.07)
Features: Implanting blastocyst, with trophoblastic cone and inner cell mass; outgrowth of endoderm (hypoblast)

Standard Witschi Stage 9, days 6.75

Features: Diplotrophoblast; inner cell mass (pendant), covered with endoderm

Day 7

Standard Witschi Stage 10, days 7.25 , Size (mm) (0.3 x 0.1)
Features: Near complete implantation; pendant begins differentiation into embryonic and extra-embryonic parts

Standard Witschi Stage 11, days 7.75 , Size (mm) (0.5 x 0.1)
Features: Completion of implantation; primary amniotic cyst; ectoplacental cone

Day 8

Standard Witschi Stage 12, days 8.5 , Size (mm) (1.04 x 0.26)
Features: Connecting ectochorionic and amniotic cavities; rudiments of amniotic folds; primitive streak; start of 3rd layer formation; blastemas of heart and pericardium

Day 9

Standard Witschi Stage 13, days 9 , Size (mm) 1.0
Features: Presomite neurula; fusion of chorio-amniotic folds, chorio-amniotic stalk; neural plate; embryo bent dorsally; bud of allantoic stalk

Standard Witschi Stage 14, days 9.5 , Size (mm) 1.5
Features: 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

Day 10

Standard Witschi Stage 15, days 10 , Size (mm) 2
Features: 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

Standard Witschi Stage 16, days 10.5 , Size (mm) 2.4
Features: Somites 13-20 (upper thoracic); 2 visceral arches; disc and yolk sac placentas; appendicular folds; embryo reverses, curves ventrally

Day 11

Standard Witschi Stage 17, days 11 , Size (mm) 3.3
Features: 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

Tail Bud Embryo

Standard Witschi Stage 18, days 11.5 , Size (mm) 3.8
Features: Somites 26-28 (upper lumbar); 3 visceral arches; arm buds recognizable

Standard Witschi Stage 19, days 11.75 , Size (mm) 4.2
Features: Somites 29-31 (lower lumbar); visceral arches I-IV; cervical folds; appendicular folds and buds

Standard Witschi Stage 20, days 11.875 , Size (mm) 5
Features: Somites 32-33 (upper sacral)

Day 12

Standard Witschi Stage 21, days 12 , Size (mm) 5.1
Features: Somites 34-35 (lower sacral); deep cervical sinuses

Standard Witschi Stage 22, days 12.125 , Size (mm) 5.2
Features: Somite 36 (1st caudal); olfactory pits

Standard Witschi Stage 23, days 12.25 , Size (mm) 5.6
Features: Somites 37-38 (caudal); start of umbilical herniation

Standard Witschi Stage 24, days 12.375 , Size (mm) 6
Features: Somites 39-40 (caudal)

Standard Witschi Stage 25, days 12.5 , Size (mm) 6.2
Features: 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

Standard Witschi Stage 26 , Size (mm) 12.75 , Size (mm) 7
Features: 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

Day 13

Standard Witschi Stage 27, days 13 , Size (mm) 8
Features: 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

Standard Witschi Stage 28, days 13.5 , Size (mm) 8.5
Features: Somites 49-51 (caudal); 1st visceral cleft transforms into external ear duct; precartilaginous condensations in handplates

Day 14

Standard Witschi Stage 29, days 14 , Size (mm) 9.5
Features: Somites 52-55 (caudal); auricular hillocks on visceral arches I and II

Standard Witschi Stage 30, days 14.5 , Size (mm) 10.5
Features: Somites 56-60 (caudal); body uncoils; mandibular precartilage; nearly round opening of external ear duct; pleuroperitoneal canal has become very narrow

Day 15

Standard Witschi Stage 31, days 15 , Size (mm) 12
Features: Somites 61-63 (caudal); facial clefts closed; pleuroperitoneal canal closed; complete diaphragm

Standard Witschi Stage 32, days 15.5 , Size (mm) 14.2
Features: Somite 64 (caudal); pinna turns forward; maximal size of umbilical hernia

Day 16

Standard Witschi Stage 33, days 16 , Size (mm) 15.5
Features: Somite 65 (usually this is last caudal); snout lifts off chest; last stage of metamorphosis

Day 17-18

Standard Witschi Stage 34, days 17-18 , Size (mm) 16-20
Features: 1st fetal stage: rapid growth of eyelids (eyes entirely covered at end of 18th day); palate complete; pinna covers ear duct; umbilical hernia withdraws

Day 19-22

Standard Witschi Stage 35, antenatal, days 19-22 , Size (mm) 20-40

Features: 2nd fetal stage: sealed eyelids; fetal membranes and placentas reach peak of development; tail grows to 10mm;

Neural System Development Pathways to the supraoptic nucleus from the brainstem and the main olfactory bulb - on the expected day of parturition, but before birth, projections from the organum vasculosum of the lamina terminalis to the supraoptic nucleus became significantly activated. PMID: 11113350

Birth occurs (22nd day in rat, 19th day in mouse)

Postnatal

Standard Witschi Stage 35, postpartum
1-16 post-partum , Size (mm) 40-1001
Features: 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

Standard Witschi Stage 36, post-natal

17+ post-partum , Size (mm) 100+1

Features: 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)