STAGE 57 Age +/- 41 d.; length 75-105 mm.

Ext. Crit.:Pigment-free spot appearing above "Stirnorgan". *Angle of elbow more than 90°; fingers stretched out in forelimb atrium, their length about 7 x their breadth*.

Int. Crit.: *First signs of cornification of epidermis at tips of 1^st, 2^nd and 3^rd toe*; stratum spongiosum and stratum compactum beginning to develop underneath stratum germinativum of skin; the later beginning to form new epidermis and numerous glands under remainder of larval epidermis in metamorphosing areas of skin; glands sinking into substratum spongiosum. *Cross section area of largest lumbar motor column nuclei of spinal cord 3-4 X that of average adjacent non-motor nuclei*. Dorso-lateral lobe of saccus endolymphaticus reaching to front end of telencephalon.

*10th and 11^th pairs of vertebral arches fused; chondrification of dorsal perichordal tube reaching vertebrally down to 10^th and intervertebrally down to 8^th vertebra*. Mm. intertransversarii developing. *Suprascapula chondrified*. Epicondyles of humerus formed; *patella ulnaris chondrified; proximal phalanges of 1^st and 2^nd finger, and proximal and middle phalanges of 3^rd and 4^th finger procartilaginous*. Musculature of radio-ulna section indicated. Left and right halves of pelvic girdle in contact with each other. *Beginning of ossification of hindlimb phalanges*. *Oocytes beginning their major growth period*.

Lip folds formed along upper and lower jaw; *anlagen of intermaxillary glands present, each with two glandular duct*; closure of branchial clefts beginning. *Beginning of metamorphosis in alimentary canal; oesophagus mucosa peeling off and first signs of histolysis in duodenum*.