5, THE ENDOCXINE PANCREAS
279
which finally results in a strong accumulation of islet tissue within Brockmann bodies (see Section 11, D, 5 and Fig. 1).
C. Cytological Characteristics and Nomenclature of the Islet Cells
With exception of the cyclostomes, all vertebrates appear to have three
functionally independent forms of islet cells: A cells, which produce
glucagon; B cells, which produce insulin; and D cells, which very likely
are the source of a third pancreatic hormone (Thomas, 1940; Epple,
1963). Concerning the nature of the secretion of the D cells, there are
presently at least two hypotheses (cf. Epple, 1965, 1968): (1) This hormone is identical with gastrin, and ( 2 ) it is specifically concerned with the
fat mobilization in the liver. The islets of many vertebrates also contain
small, agranular cells which were first described by Bensley (1911) as
C cells in the guinea pig. At least some fishes and amphibia have “amphiphil” cells which very likely represent intergrade stages between two
types of granular islet cells (see Section 11, D, 5,c). Two groups of fishes
possess peculiar cell types of unknown function which have not yet been
identified in other animals with certainty: The cyclostomes have gomori
negative granular cells which electron microscopically contain empty
vesicles. The holocephalians have many argyrophil X cells.
Unfortunately, the nomenclature of the islet cells is even more confusing than their number (cf. Bargmann, 1939; Mosca, 1959; Epple, 1968;
Fujita, 1968). In fishes, the only nomenclatural daculty so far is offered
by the use of the terms “A and D cell.” Hellman, Hellerstrom and their
co-workers differentiate between A, and A, cells (Hellman and Hellerstrom, 1968). The A, cells of Hellman and Hellerstriim (1960) are
identical with the D cells in the nomenclature of this article, while their
A, cells are here termed “A cells.”
D. Comparative Islet Histophysiology of the Fishes
1. CYCLOSTOMATA
The islet organ of the cyclostomes is represented by an aggregation of
small lobules which are surrounded by connective tissue (cf. Barrington,
1945; Ermisch, 1966; Falkmer and Winbladh, 1964a; Schirner, 1963a,b).
Intralobular cavities are common in ammocoetes and less abundant in
adult lampreys (Ermisch, 1966; Winbladh, 1966). In Myxine, they are
often absent in smaller specimens ( Falkmer and Winbladh, 1964a).
In Petromyzon, the endocrine tissue is located dorsally and ventrally
279
which finally results in a strong accumulation of islet tissue within Brockmann bodies (see Section 11, D, 5 and Fig. 1).
C. Cytological Characteristics and Nomenclature of the Islet Cells
With exception of the cyclostomes, all vertebrates appear to have three
functionally independent forms of islet cells: A cells, which produce
glucagon; B cells, which produce insulin; and D cells, which very likely
are the source of a third pancreatic hormone (Thomas, 1940; Epple,
1963). Concerning the nature of the secretion of the D cells, there are
presently at least two hypotheses (cf. Epple, 1965, 1968): (1) This hormone is identical with gastrin, and ( 2 ) it is specifically concerned with the
fat mobilization in the liver. The islets of many vertebrates also contain
small, agranular cells which were first described by Bensley (1911) as
C cells in the guinea pig. At least some fishes and amphibia have “amphiphil” cells which very likely represent intergrade stages between two
types of granular islet cells (see Section 11, D, 5,c). Two groups of fishes
possess peculiar cell types of unknown function which have not yet been
identified in other animals with certainty: The cyclostomes have gomori
negative granular cells which electron microscopically contain empty
vesicles. The holocephalians have many argyrophil X cells.
Unfortunately, the nomenclature of the islet cells is even more confusing than their number (cf. Bargmann, 1939; Mosca, 1959; Epple, 1968;
Fujita, 1968). In fishes, the only nomenclatural daculty so far is offered
by the use of the terms “A and D cell.” Hellman, Hellerstrom and their
co-workers differentiate between A, and A, cells (Hellman and Hellerstrom, 1968). The A, cells of Hellman and Hellerstriim (1960) are
identical with the D cells in the nomenclature of this article, while their
A, cells are here termed “A cells.”
D. Comparative Islet Histophysiology of the Fishes
1. CYCLOSTOMATA
The islet organ of the cyclostomes is represented by an aggregation of
small lobules which are surrounded by connective tissue (cf. Barrington,
1945; Ermisch, 1966; Falkmer and Winbladh, 1964a; Schirner, 1963a,b).
Intralobular cavities are common in ammocoetes and less abundant in
adult lampreys (Ermisch, 1966; Winbladh, 1966). In Myxine, they are
often absent in smaller specimens ( Falkmer and Winbladh, 1964a).
In Petromyzon, the endocrine tissue is located dorsally and ventrally