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CAMBRIAN PERIOD

542-488 million years ago

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chordate glands

ENDOCRINE SYSTEM

Ancestral cephalochordates possessed homologs of the hypothalamus, pituitary gland, pineal gland, and thyroid gland. Insulin-like molecules were secreted from the digestive tract.

In Amphioxus, the dorsal portion of the oral region includes Hatschek's pit and groove which are homologous to the hypothalamus and pituitary of vertebrates. Hatschek's pit contains hormones similar to GnRH, LH, human chorionic gonadotropin, substance P, met-enkephalin, CCK, and gastrin. It is not only capable of stimulating the gonads in Amphioxus, but also in toads. The homology of the pituitary to Hatschek's pit supports the hypothesis that the pituitary evolved from a chemosensitive olfactory region (Gorbman, 1995; Ruppert, from Harrison, 1997, p. 413.; Stach, 2000). Islet1 expression also reveals that Amphioxus may have homologs of the pineal gland and adenohypophysis (Jackman, 2000).

Lancelets produce iodothyronine hormones and a protein similar to thyroglobulin in its endostyle (Stach, 2000; Ruppert, from Harrison, 1997, p. 440)

Lancelets have a molecule which shares characteristics of insulin and insulin-like peptide and may be a transitional form between the two (Chan, 1990). In lancelets, the endocrine cells which produce this insulin-like hormone are located in the GI tract but not until hagfish do they form a separate islet organ (Youson, 1999).