STAGE 61 Age +/- 48 d.

Ext. Crit.: Head narrower. Tentacles considerablshortened, mostly curved backwards. *Length of n. olfactorius equal to diameter of bulbus olfactorius*. *4th arterial arch seen just in front of adult skin area of forelimb*. Openings of gill chambers considerably narrowed. *Forelimb at level of posterior half of heart*. Adult skin area on abdomen covering posterior half of heart*. *Fins considerably reduced*.

Int. Crit.: *Metamorphosis of adult skin areas completed; adult skin area of trunk covering entire brain cavity and caudal portion of heart*. *Spinal gangl. 8 descended to level well posterior to root of gangl. 9, and nearly all of gangl. 9 posterior to lumbar level of spinal cord*. Finger-like protrusions developed from lateral cavity of olfactory organ.

*Appearance of pars media and externa plectri and annulus tympanicus as mesenchymatous condensations*; erosion phenomena infloor and side walls of cranium and in palatoquadratum and hyobranchal apparatus; *angle between palatoquadratum and anterior floor of cranium 50°*. Reduction of pars lateralis of m. levator mandibulae anterior; m. interhyoideus attached to ceratohyale and palatoquadratum. * 11^th pair of vertebral arches partially ossified perichondrally*. Mm. sterno-hyoidei fused to unpaired anlage. *Degenerative hypertrophy of skin at end of tail; atrophy of fins and posterior tail notochord*. *Paired sternal anlage partially cartilaginous*. *Epipubis anlagen fused to Y-shaped cartilage*. 1^st nephron of pronephros completely disappeared.

First signs of degeneration of filter apparatus; *middle ear cavity shifted to position somewhat cranial to eye*, tuba pharyngo-tympanica opening into oro-pharyngeal cavity at level of caudal part of eye. *Histolysis in pyloric part of stomach and in ileum*.