STAGE 43 Age 3 d., 15 h.; length 7.5-8.3 mm.

Ext. Crit.: Lateral line system becoming visible externally. Cement gland losing its pigment. *Torsion of intestine about 180°*; proctodeum narrower, arched or S-shaped.

Int. Crit.: Ventral lateral line has reached pre-anal fin. Beginning of development of cerebral hemispheres; *first signs of choroid plexus formation in pros- and rhombencephalic roof*. Narrow cell strand connecting lateral part of nasal organ with pharyngeal roof. Beginning of formation of pectinate membrane of eye. *Latero-cranial sensorial anlage of ear vesicle split into anlagen of crista anterior and macula utriculi*.

Beginning of chondrification of cranium; cartilagines Meckeli, ceratohyale and basihyobranchiale chondrified*. Hindlimb region indicated. *Anterior and posterior valves capable of closing atri-ventricular aperture of heart*. Accumulation of mesenchyme indicating future spleen anlage. Continuous mesonephric anlage formed. Primordial germ cells beginning to form median, unpaired genital ridge.

Hypochorda disappeared. Epithelial bodies indicated on ventral side of 3^rd and 4^th visceral pouches. *Long intestinal loop formed, reaching anteriorly as far as liver*.