STAGE 49 Age +/- 12 d.; length 17-23 mm.

Ext. Crit.: Melanophores usually appearing around thymus gland and nerves and blood vessels of head; xanthophores appearing on pericard. Forelimb bud distinct. *Hindlimb bud somewhat longer, distal outline still circular, no constriction at base*. Melanophores appearing on dorsal and ventral fins.

Int. Crit.: *Appearance of bilateral telencephalic choroid invaginations*; infundibular process of neurohypophysis beginning to develop; first anlage of tuberal part of adenohypophysis; *small tubular anlage of paraphysis; at least five nuclear layers in optic tectum*; first cells of molecular layer of cerebellum formed; choroid plexus formation reaching lateral border of rhombencephalon. N. abducens discernable. *Semicircular canals with ampullae completed; macula lagenae located in separate diverticulum of sacculus; saccus perilymphaticus extending into for. jugulare*.

*Formation of canales semicircularens anterior and lateralis of ear capsule*. Cartilaginous connection between occipital arch and ear capsule. *10-12 pairs of functional mesonephric units and 6-8 pairs of glomeruli formed*; second generation of mesonephric tubules and glomeruli appearing. Scattered cells from mesonephric and interrenal blastemata entering genital ridges. *Taste buds appearing in epithelium of primitive tongue* and in lateral regions of oro-pharyngeal roof; *follicle formation starting in thyroid gland*. Colon segregating from intestine.