286
AUGUST EPPLE
The histology of the teleost islets appears similarly complex to that
of the selachians. As already shown by Bowie (1925), there are at least
three forms of granular cells. Recent studies revealed A, B, and D cells
in all species investigated (Falkmer and Hellman, 1961; Kenikar, 1963;
Mosca and Solcia, 1964; Falkmer, 1965a, 1966; Epple, 1965, 1967; Honma
and Tamura, 1968; Khanna and Mehrotra, 1969). The electron microscopic studies showed the existence of A and B cells in all teleosts investigated so far. Falkmer and Olsson (1962) found five ultrastructurally
different cell types in Cottus scorpius. Titlbach (1966) observed A, B,
and D cells; Bencosme et al. (1965) found a few granules in the D cells,
while Watanabe (1960) was able to identify D granules only with the
light microscopy. Like et al. (1964) observed A, B, and agranular cells
and considered the latter elements as progenitors of the B cells. The
observation that Tilapia mossambica only has B cells (Sivadas, 1964)
could not be confirmed (Sivadas, in litt.; Epple, 1965; Falkmer, 1965a).
In some species, e.g., Cottus scorpius (Falkmer et al., 1964a) and Scorpaenu scrofa (Mosca and Solcia, 1964), large numbers of agranular ( C )
cells are found. They are rare in Salmo trutta (Schneider and Epple,
1%9), and apparently absent in Saluelinus leucomaenis pludus (Honma
and Tamura, 1968). Amphiphils have been described so far in TiZuapia
mossambica ( Epple, 1965), Salmo trutta (Epple, 1967), and Saluelinus
leucomaenis pluuius ( Honma and Tamura, 1968). Histochemically, the
A cells show a positive reaction to tryptophan (Falkmer, 1966; Mosca and
Solcia, 1964); in Zctalurus, they also contain glycogen (Bencosme et al.,
1965). The B cells of Opsanus tau (Lazarow, 1963), Cyprinus carpi0
( Watanabe, 1960), and Zctalurms nebubsus (Bencosme et al., 1965) contain glycogen. Further data on the histochemistry of the teleost islets are
given by Pallot et al. (1957) and Schatzle (1958). The islets of the
teleosts are rich in zinc (cf. Weitzel et al., 1953; Maske et al., 1956; J.
Davidson, 1958). In Cottus scorpius, this material is restricted to a central
islet region which contains B and D cells (Falkmer et al., 1964a). In
Cottus quadricomis, Pihl (1967) was able to localize heavy metal electron
microscopically within the B granules. Various authors observed intracellular colloid droplets in A and/or B cells; although these structures
were studied very thoroughly by histochemical techniques, their function
is still obscure (cf. Ermisch, 1967).
Since the pioneer study of Macleod (1922), more than sufficient
evidence for insulin within the teleost islets has been accumulated (see
Section 11, E, 1 ) . The occurrence of glucagon is mainly concluded from
biological effects of islet extracts; immunological evidence for this hormone was presented by Falkmer (1965a, 1966) (see Section 11, E, 2).
AUGUST EPPLE
The histology of the teleost islets appears similarly complex to that
of the selachians. As already shown by Bowie (1925), there are at least
three forms of granular cells. Recent studies revealed A, B, and D cells
in all species investigated (Falkmer and Hellman, 1961; Kenikar, 1963;
Mosca and Solcia, 1964; Falkmer, 1965a, 1966; Epple, 1965, 1967; Honma
and Tamura, 1968; Khanna and Mehrotra, 1969). The electron microscopic studies showed the existence of A and B cells in all teleosts investigated so far. Falkmer and Olsson (1962) found five ultrastructurally
different cell types in Cottus scorpius. Titlbach (1966) observed A, B,
and D cells; Bencosme et al. (1965) found a few granules in the D cells,
while Watanabe (1960) was able to identify D granules only with the
light microscopy. Like et al. (1964) observed A, B, and agranular cells
and considered the latter elements as progenitors of the B cells. The
observation that Tilapia mossambica only has B cells (Sivadas, 1964)
could not be confirmed (Sivadas, in litt.; Epple, 1965; Falkmer, 1965a).
In some species, e.g., Cottus scorpius (Falkmer et al., 1964a) and Scorpaenu scrofa (Mosca and Solcia, 1964), large numbers of agranular ( C )
cells are found. They are rare in Salmo trutta (Schneider and Epple,
1%9), and apparently absent in Saluelinus leucomaenis pludus (Honma
and Tamura, 1968). Amphiphils have been described so far in TiZuapia
mossambica ( Epple, 1965), Salmo trutta (Epple, 1967), and Saluelinus
leucomaenis pluuius ( Honma and Tamura, 1968). Histochemically, the
A cells show a positive reaction to tryptophan (Falkmer, 1966; Mosca and
Solcia, 1964); in Zctalurus, they also contain glycogen (Bencosme et al.,
1965). The B cells of Opsanus tau (Lazarow, 1963), Cyprinus carpi0
( Watanabe, 1960), and Zctalurms nebubsus (Bencosme et al., 1965) contain glycogen. Further data on the histochemistry of the teleost islets are
given by Pallot et al. (1957) and Schatzle (1958). The islets of the
teleosts are rich in zinc (cf. Weitzel et al., 1953; Maske et al., 1956; J.
Davidson, 1958). In Cottus scorpius, this material is restricted to a central
islet region which contains B and D cells (Falkmer et al., 1964a). In
Cottus quadricomis, Pihl (1967) was able to localize heavy metal electron
microscopically within the B granules. Various authors observed intracellular colloid droplets in A and/or B cells; although these structures
were studied very thoroughly by histochemical techniques, their function
is still obscure (cf. Ermisch, 1967).
Since the pioneer study of Macleod (1922), more than sufficient
evidence for insulin within the teleost islets has been accumulated (see
Section 11, E, 1 ) . The occurrence of glucagon is mainly concluded from
biological effects of islet extracts; immunological evidence for this hormone was presented by Falkmer (1965a, 1966) (see Section 11, E, 2).