STAGE 39 Age 2 d., 8 ½ h.; length 5.9-6.5 mm.

Ext. Crit.: Melanophores appearing around nasal pits. Opening of stomodeal invagination transversely elongated. Melanophores on back arranges in a superficial and a deep layer. *Outlines of proctodeum and tail myotomes forming angle of about 135°*. Melanophores appearing along ventral edge of tail musculature.

Int. Crit.:Infraorbital lateral line anlagen segregating into sense organs. *First fibers in comm. Anterior*. N. hyomandibularis VII connected with m. interhyoideus; gangl. superius IX and gangl. petrosum IX separated; *roots of n. vagus distinct*; Thin layer of fibers on ventral surface of spinal cord; a few cells of central gray matter bulging into white matter in anterior levels of spinal cord. *Arteria hyaloidea has reached interior of eye cup*; delicate layer of mesenchyme around eye cup; eye muscle anlagen outlined. *Sensorial epithelium of ear vesicle split into medio-caudal and latero-cranial anlage*.

*About 43 post-otic somites*. *6^th aortic arch completed with ductus Botalli and pulmonary artery*. First mesonephric cells appearing in caudal trunk region.

*Contact between ectoderm and entoderm obliterated in 1^st and 2^nd visceral pouch*; 1^st visceral pouch representing anlage of middle ear and tuba Eustachii; anlage of primitive tongue formed; cavities of trachea and pharynx separated by horizontal ridge. Duodenum curving to the left side as *first symptom of coiling of intestinal tract*; most posterior part of postanal gut disintegrating.