STAGE 64 Age +/- 53 d.

Ext. Crit.: Corner of mouth well behind eye. *Various adult skin areas joined almost everywhere, borderlines still clearly visible*. *Length of tail (from anus) 1/3 of body length*.

Int. Crit.: *Root of spinal gangl. 7 anterior to gangl. 6*.

Appearnace of adult proc. oticus; *pars media and externa plectri confluent; angle between palatoquadratum and anterior floor of cranium 105°*; branchial chambers disappeared. Formation of adult m. levator mandibulae posterior; mm. constrictores branchiales, mm. sub arcuales recti and m. transversus ventralis disappeared. *Entire cartilage formation of ventral perichordal tube converted into loose connective tissue and cartilage of lateral perichordal tube in process of resorption*. Degerneration of notochord started in urostyle region; *only about 14 postotic muscle segments distinguishable*. *Paired sternal anlage fused*. *4^th aortic arch (adult aorta) larger than 3^rd (larval aorta)*. Disappearance of branchial veins and branchial branches of external jugulars. Pronephros completely disappeared. Primordia of Mullerian ducts developing. Cranial margin of mouth slit situated caudal to level of nostrils; *thymus gland moved to position ventro-lateral to ear capsule*. *Epithelium of pyloric portion of stomach and of colon reconstituted; new glandular elements in oesophagus, duodenum and ileum*.