anus not differentiated), lying dorsally to a large yolk-sac (Fig. 4A).
During yolk-sac absorption (1–2 dph), the rudimentary digestive
system became differentiated into buccopharynx, esophagus, and
intestine. By 3 dph the mouth was open, the swim bladder was
differentiated, the liver continued to develop, and the posterior
intestine and some connective tissue became visible (Fig. 4B).
Histological analyses revealed that the urinary duct, swim bladder,
intestine, liver, and pancreas were all developed by 3 dph, and by
8 dph basophilic cells of the diffuse exocrine pancreas were visible
and the intestine was lined by ciliated columnar epithelial cells with
basal nuclei (Fig. 4C).