STAGE 63 Age +/- 51 d.

Ext. Crit.: *Head narrower than trunk*. Tentacles mostly disappeared. *Corner of mouth at level of caudal border of eye*. "Laraval aorta" and thymus gland no longer externally visible. *Operculum closed*. Adult skin area on abdomen and lower jaw separated by narrow band larval skin. *Forelimb at level of anterior half of heart*. Fin mostly perforated near anus. *Tail still slightly longer than body*.

Int. Crit.: Area of larval skin between upper jaw and trunk areas of adult skin disappeared for greater part. *Root of spinal gangl. 9 just posteriorly to gangl. 7*. Naso-lachrymal duct opening on tip of papilla. Disappearance of proc. muscularis capsulae auditivae; *for. metopticum confluent with for. caroticum; disappearance of proc. cornu-quadratus lateralis, proc. ascendens, larval proc. oticus and medial portion of comm. quadrato-cranialis anterior; pars interna and media plectri cartilaginous; angle between palatoquadratorum and anterior floor of cranium 85°; appearance of post-palatine commissure and pterygoid*; formation of proc. pterygoideus; beginning of reduction of branchial chambers. M. orbito-hyoideus fused with m. suspensorio-hyoideus. *Cartilage of 13^th pair of vertebral arches and cartilage of anterior ventral perichordal tube degenerating*; hypochord reaching to 13^th vertebra. *In tail, chordal epithelium degenerating and entire notochord shrivelling; beginning of actual degeneration of muscle segments (still 49 post-otic muscle segments distinguishable)*. *Alae sterni forming*. *Ductus caroticus disappeared*. *3^rd nephrostome of pronephros fused with ostium tubae*. Operculum a shapeless mass; *gill slits still closed*. Middle ear lying against ear capsule; anlage of tympanic membrane formed. *Intestinal helix making only 1 ½ irregular revolutions*; typhylosole extending up to short distance from beginning of colon; *histolysis in colon*.