380
D. HAROLD COPP
maeroids, and elasmobranchs have only a cartilaginous skeleton while
many bony fishes have acellular bone which is incapable of remodeling
(Kolliker, 1859; Moss, 19fX). However, control of plasma calcium is apparent even in the most primitive fishes (Urist, 1962, 1986). As seen in
Table I, the hagfish maintains a serum calcium about half that of seawater, while the lamprey has a concentration almost the same as that of
man, These cyclostomes lack all three of the important factors present
in terrestrial vertebrates (bone, parathyroid, and ultimobranchial) and
apparently regulate body calcium in an open system through controlled
transfdr across gill membranes ( Urist, 1962).
The chimaeroids and elasmobranchs (Urist, 1966) also contain no
true bone, and presumably control calcium through membrane mechanisms; however, in these fishes the ultimobranchial glands first appear and
contain the hormone, calcitonin (Copp et al., 1967b), which in higher
vertebrates acts to control hypercalcemia. This gland may develop in
response to the high calcium environment in the sea. Calcitonin can
hardly act on bone resorption, since there is none, but it may possibly
facilitate appropriate calcium transport mechanisms and so participate in
calcium regulation. This would also apply to teleosts with acellular bone.
11. ULTIMOBRANCHIAL GLANDS
Until very recently, the function of the ultimobranchial glands was
unknown (Copp, 1967). The association of these glands with calcitonin
and calcium regulation is one of the exciting developments in comparative
endocrinology ( Copp, 1969a). The ultimobranchial glands (also referred
to as postbranchial, suprapericardial, or ultimobranchial bodies) were
the first of the calcium-regulating glands to develop for they are found in
all jawed vertebrates (including chimaeroids, elasmobranchs, and teleosts ) , while the parathyroids are found only in terrestrial vertebrates. The
ultimobranchial has not been demonstrated in cyclostomes (Watzka,
1933). As shown in Fig. 1, it develops embryologically from the epithelium of the last or “ultimate” gill pouch. The parathyroid glands
develop in higher vertebrates from a very similar position in gill pouches
4 and 5.
A. History
The gland was first described by van Bemmelen (1886) in elasmobranchs and chimaeroids. He referred to them as “suprapericardial bodies”
D. HAROLD COPP
maeroids, and elasmobranchs have only a cartilaginous skeleton while
many bony fishes have acellular bone which is incapable of remodeling
(Kolliker, 1859; Moss, 19fX). However, control of plasma calcium is apparent even in the most primitive fishes (Urist, 1962, 1986). As seen in
Table I, the hagfish maintains a serum calcium about half that of seawater, while the lamprey has a concentration almost the same as that of
man, These cyclostomes lack all three of the important factors present
in terrestrial vertebrates (bone, parathyroid, and ultimobranchial) and
apparently regulate body calcium in an open system through controlled
transfdr across gill membranes ( Urist, 1962).
The chimaeroids and elasmobranchs (Urist, 1966) also contain no
true bone, and presumably control calcium through membrane mechanisms; however, in these fishes the ultimobranchial glands first appear and
contain the hormone, calcitonin (Copp et al., 1967b), which in higher
vertebrates acts to control hypercalcemia. This gland may develop in
response to the high calcium environment in the sea. Calcitonin can
hardly act on bone resorption, since there is none, but it may possibly
facilitate appropriate calcium transport mechanisms and so participate in
calcium regulation. This would also apply to teleosts with acellular bone.
11. ULTIMOBRANCHIAL GLANDS
Until very recently, the function of the ultimobranchial glands was
unknown (Copp, 1967). The association of these glands with calcitonin
and calcium regulation is one of the exciting developments in comparative
endocrinology ( Copp, 1969a). The ultimobranchial glands (also referred
to as postbranchial, suprapericardial, or ultimobranchial bodies) were
the first of the calcium-regulating glands to develop for they are found in
all jawed vertebrates (including chimaeroids, elasmobranchs, and teleosts ) , while the parathyroids are found only in terrestrial vertebrates. The
ultimobranchial has not been demonstrated in cyclostomes (Watzka,
1933). As shown in Fig. 1, it develops embryologically from the epithelium of the last or “ultimate” gill pouch. The parathyroid glands
develop in higher vertebrates from a very similar position in gill pouches
4 and 5.
A. History
The gland was first described by van Bemmelen (1886) in elasmobranchs and chimaeroids. He referred to them as “suprapericardial bodies”