STAGE 37/38 Age 2 d., 5 ½ h.; length 5.6-6.2 mm.

Ext. Crit.: Stomodeal invagination much deeper, oepning round. *Both gill rudiments nipple-shaped, a branch of the anterior one indicated*. *Posterior outline of proctodeum straight, forming very obtuse angle with ventral border of tail myotomes*. Melanophores spreading over tail.

Int. Crit.: Appearance of anlagen of occipital and ventral trunk lateral lines. Sub-commissural organ differentiating; *first fibers of comm. Posterior*. N branchialis X² has reached middle of 2^nd branchial arch. *Rhohon-beard cells appearing in anterior tail levels of spinal cord*. Beginning of aggregation of spinal ganglion cells. *Organon vomero-nasale segregated from main olfactory organ*. Nuclei arranged in three layers in pars optica retinae; beginning og differentiation of visual cells.

Anlagen of m. quadrato-hyoangularis and m. orbito-hyoideus segregated. *About 40 post-otic somites formed*. Paired dorsal aorta extending forwards as internal carotid artery; median dorsal aorta extending backwards into tail as caudal artery. Future dorsal branch of caudal vein appearing in dorsal tail fin. *Wolffian ducts and rectal diverticula communicating*; entire pronephros functional.

Stomach and duodenum dorsally segregated; anterior wall of primary liver cavity forming numerous folds; *the two ventral pancreas anlagen discernable*.