5. THE ENDOCRINE P A N W A S
283
An early attempt to demonstrate insulin in cyclostomes failed (Maskell, 1930). Recently, insulin was extracted from Myxine (cf. F a k e r and
Wilson, 1967; Weitzel et al., 1967). Neither glucagon (Falkmer, 1966;
Weitzel et al., 1967) nor gastrin (Blair et al., 1968) could be demonstrated.
2. ELASMOBRANCHII
The compact pancreas of the elasmobranchs (cf. Bargmann, 1939)
contains both exocrine and endocrine tissue. The endocrine tissue occurs
mainly as an outer layer along the epithelium of smaller ducts or as single
cells at the basis of larger ducts ( cf. Bargmann, 1939; Thomas, 1940;
Clausen, 1953; Kern, 1964; Ferner and Kern, 1964; Ostberg et al., 1966;
Epple, 1967). As shown by Oppel (1900), in some species (e.g., Raja
asterias and Squalus acanthias) isletlike configurations are found (cf.
Bargmann, 1939; Thomas, 1940; Patent, 1968). The failure of Kern ( 1964)
and Ferner and Kern (1964) to find isletlike arrangements in their
material possibly results from seasonal factors or the age of their animals.
Howbeit, the islet tissue of the elasmobranchs shows striking similarity to
the early ontogenetic stages of the islet formation in the human (see, e.g.,
Neubert, 1927).
There are A, B, D, and agranular cells (Thomas, 1940; 0stberg.et al.,
1966) as well as amphiphils (Epple, 1967; Patent, 1MS). This suggests
the existence of insulin, glucagon, and at least one more islet hormone.
Tryptophan was found histochemically in the A cells (Kern, 1964; Ferner
and Kern, 1964); glucagon has not yet been demonstrated (Falkmer,
1965a, 1966). Macleod (1922) was the first to extract insulin from the
elasmobranchs. McCormick (19%) obtained the highest yield of insulin
in elasmobranchs from Raja. In Squulus, the ventral lobe of the pancreas
contained less insulin than the dorsal lobe ( McCormick and Noble, 1925).
Elasmobranch insulin was also found during recent investigations (see
Section 11, E, 1). A small quantity of gastrinlike activity was detected in
an extract of a skate pancreas ( Blair et al., 1968).
3. HOLOCEPHALI
The pancreas of the holocephalians is likewise compact but contains
many islets which often have a close relationship to the excretory ducts.
A, B, D, and peculiar X cells occur (Fujita, 1962,1964; Patent and Epple,
1967). The X cells have not been shown with certainty to occur in other
vertebrates (cf. Patent, 1968); they make up about 50% of all islet cells in
holocephalians and exhibit the characteristic features of secretorily active
cells (Patent and Epple, 1967). Recently, Patent (1!368) extracted insulin
from the holocephalian pancreas.
283
An early attempt to demonstrate insulin in cyclostomes failed (Maskell, 1930). Recently, insulin was extracted from Myxine (cf. F a k e r and
Wilson, 1967; Weitzel et al., 1967). Neither glucagon (Falkmer, 1966;
Weitzel et al., 1967) nor gastrin (Blair et al., 1968) could be demonstrated.
2. ELASMOBRANCHII
The compact pancreas of the elasmobranchs (cf. Bargmann, 1939)
contains both exocrine and endocrine tissue. The endocrine tissue occurs
mainly as an outer layer along the epithelium of smaller ducts or as single
cells at the basis of larger ducts ( cf. Bargmann, 1939; Thomas, 1940;
Clausen, 1953; Kern, 1964; Ferner and Kern, 1964; Ostberg et al., 1966;
Epple, 1967). As shown by Oppel (1900), in some species (e.g., Raja
asterias and Squalus acanthias) isletlike configurations are found (cf.
Bargmann, 1939; Thomas, 1940; Patent, 1968). The failure of Kern ( 1964)
and Ferner and Kern (1964) to find isletlike arrangements in their
material possibly results from seasonal factors or the age of their animals.
Howbeit, the islet tissue of the elasmobranchs shows striking similarity to
the early ontogenetic stages of the islet formation in the human (see, e.g.,
Neubert, 1927).
There are A, B, D, and agranular cells (Thomas, 1940; 0stberg.et al.,
1966) as well as amphiphils (Epple, 1967; Patent, 1MS). This suggests
the existence of insulin, glucagon, and at least one more islet hormone.
Tryptophan was found histochemically in the A cells (Kern, 1964; Ferner
and Kern, 1964); glucagon has not yet been demonstrated (Falkmer,
1965a, 1966). Macleod (1922) was the first to extract insulin from the
elasmobranchs. McCormick (19%) obtained the highest yield of insulin
in elasmobranchs from Raja. In Squulus, the ventral lobe of the pancreas
contained less insulin than the dorsal lobe ( McCormick and Noble, 1925).
Elasmobranch insulin was also found during recent investigations (see
Section 11, E, 1). A small quantity of gastrinlike activity was detected in
an extract of a skate pancreas ( Blair et al., 1968).
3. HOLOCEPHALI
The pancreas of the holocephalians is likewise compact but contains
many islets which often have a close relationship to the excretory ducts.
A, B, D, and peculiar X cells occur (Fujita, 1962,1964; Patent and Epple,
1967). The X cells have not been shown with certainty to occur in other
vertebrates (cf. Patent, 1968); they make up about 50% of all islet cells in
holocephalians and exhibit the characteristic features of secretorily active
cells (Patent and Epple, 1967). Recently, Patent (1!368) extracted insulin
from the holocephalian pancreas.