STAGE 47 Age 5 d., 12 h.; length 12-15 mm.

Ext. Crit.: Tentacles larger. *Edge of operculum forming quarter of a circle*. Xanthophores forming opaque layer on abdomen. *Intestine showing 2 ½ - 3 ½ revolutions. Hindlimb bud more distinct*.

Int. Crit.: Cement gland beginning to degenerate. *Prosencephalic plexus branched*; pars intermedia of adenohypophysis beginning to differentiate. *2-3 Jacobson's gland anlagen discernable on organon vomero-nasale*. *Formation of posterior, and beginning of formation of anterior semicircular canal*; formation of maculae lagenae and sacculi and of papillae aphibiorum and basilaris; saccus endolymphaticus strongly lobed and apposed to choroid plexus of Ivth ventricle; beginning of formation of perilymphatic system.

Chondrification of crista otica and proc. muscularis casulae auditivae; lateral wall of ear capsule only pierced by for. ovale; for. jugulare and prooticum completed by procartilaginous connections. *Head somite IV disappeared and trunk somite I reduced*. *Forelimb atrium formed*. Secondary vessels of 3^rd and 4^th aortic arches disappeared. Appearance of blood corpusclesin spleen anlage. Pronephros free of yolk; caudal end of pronephros and cranial end of mesonephric anlage have reached each other; *6-8 mesonephric units segregated, central lumen in oldest units*; anlagen of first glomeruli appearing. Genital ridges beginning to protrude into coelomic cavity. External gills degenerated to great extent. First indication of pyloric part of stomach; intestinal coils arranged in outer and inner spiral.