5. THE ENDOCRINE PANCREAS
285
tracted (see Section 11, E, 1, c). The pancreas of Lepisosteus is less disseminated than that of Amiu and Acipemer (cf. Oppel, 1900).
c. Tebostei. Contrary to popular belief, the Brockmann bodies usually
do not contain only pure islet tissue. As stressed by Baron (1934) and
Bargmann (1939), in many cases they consist of a giant islet which often
is separated from a more or less complete rim of exocrine tissue by a
connective tissue sheet. The connective tissue capsule is not always complete (cf. Bargmann, 1939; Falkmer, 1961,1966), and exocrine tissue may
occur even within the capsule (Murrel and Nace, 1959; Lazarow, 1963;
Bencosme et al., 1965). Thus the name “principal islet” (Rennie, 1903)
is misleading.
In accordance with Siwe (1926), Baron (1934) considers the Brockmann bodies as direct derivatives of the dorsal epithelium of the embryonic gut, (see also Vorstman, 1948). He furthermore assumes that in
postembryonic life the islets in the derivatives of the ventral pancreas
“anlagen” develop from ducts. This latter conclusion is supported by the
observations of Dancasiu ( 1960). To some extent, the Brockmann bodies
may correspond to the splenic portion of the avian and reptilian pancreas
(Clara, 1924; Miller, 1962), which are also extremely rich in islet tissue.
It is possible to free the endocrine components of the Brockmann
bodies from the other tissues (cf. Falkmer, 1961; Hellman and Larsson,
1961; Lazarow, 1963 ) . However, histological controls are prerequisite
when islet material from a new species is to be collected for biochemical
studies, especially since cysts of nematodes ( Macleod, 1922; Bargmann,
1939) or lymphatic tissue (Baron, 1934) have on appearance similar to
pancreas nodules. Favorable species for the collection of islet material
are Cottus scorpius ( Falkmer, 1961), Cottus quadricornis ( Hellman and
Larsson, 1961 ) , Opsanus tau ( Humbel and Renold, 1963), and especially
Lophius piscatorius (Macleod, 1922; Weitzel et al., 1953; Bauer et al.,
1965). The tuna, Thunnus thynnus, has two especially large Brockmann
bodies with a different B cell content and correspondingly different
amounts of insulin (cf. Planas and Garcia, 1964). Further information on
the occurrence of both pancreas tissues in teleosts may be obtained from
the classic papers of Rennie ( 1905) McCormick ( 1925), and Siwe ( 1926),
and from the critical studies of Baron (1934), Broman (1937), and
Bargmann ( 1939).
It is clear from the morphology of the teleost pancreas that investigations on the effects of “isletectomy” by removal of the Brockmann bodies
must take into consideration the existence of islets at other sites. Maybe
a complete removal of the islets and of all potentially insulogenic tissue
is only possible in species which have a “compact” pancreas (e.g., Anguillu
vulgaris; cf. Macleod, 1922), but then this would be pancreatectomy.
285
tracted (see Section 11, E, 1, c). The pancreas of Lepisosteus is less disseminated than that of Amiu and Acipemer (cf. Oppel, 1900).
c. Tebostei. Contrary to popular belief, the Brockmann bodies usually
do not contain only pure islet tissue. As stressed by Baron (1934) and
Bargmann (1939), in many cases they consist of a giant islet which often
is separated from a more or less complete rim of exocrine tissue by a
connective tissue sheet. The connective tissue capsule is not always complete (cf. Bargmann, 1939; Falkmer, 1961,1966), and exocrine tissue may
occur even within the capsule (Murrel and Nace, 1959; Lazarow, 1963;
Bencosme et al., 1965). Thus the name “principal islet” (Rennie, 1903)
is misleading.
In accordance with Siwe (1926), Baron (1934) considers the Brockmann bodies as direct derivatives of the dorsal epithelium of the embryonic gut, (see also Vorstman, 1948). He furthermore assumes that in
postembryonic life the islets in the derivatives of the ventral pancreas
“anlagen” develop from ducts. This latter conclusion is supported by the
observations of Dancasiu ( 1960). To some extent, the Brockmann bodies
may correspond to the splenic portion of the avian and reptilian pancreas
(Clara, 1924; Miller, 1962), which are also extremely rich in islet tissue.
It is possible to free the endocrine components of the Brockmann
bodies from the other tissues (cf. Falkmer, 1961; Hellman and Larsson,
1961; Lazarow, 1963 ) . However, histological controls are prerequisite
when islet material from a new species is to be collected for biochemical
studies, especially since cysts of nematodes ( Macleod, 1922; Bargmann,
1939) or lymphatic tissue (Baron, 1934) have on appearance similar to
pancreas nodules. Favorable species for the collection of islet material
are Cottus scorpius ( Falkmer, 1961), Cottus quadricornis ( Hellman and
Larsson, 1961 ) , Opsanus tau ( Humbel and Renold, 1963), and especially
Lophius piscatorius (Macleod, 1922; Weitzel et al., 1953; Bauer et al.,
1965). The tuna, Thunnus thynnus, has two especially large Brockmann
bodies with a different B cell content and correspondingly different
amounts of insulin (cf. Planas and Garcia, 1964). Further information on
the occurrence of both pancreas tissues in teleosts may be obtained from
the classic papers of Rennie ( 1905) McCormick ( 1925), and Siwe ( 1926),
and from the critical studies of Baron (1934), Broman (1937), and
Bargmann ( 1939).
It is clear from the morphology of the teleost pancreas that investigations on the effects of “isletectomy” by removal of the Brockmann bodies
must take into consideration the existence of islets at other sites. Maybe
a complete removal of the islets and of all potentially insulogenic tissue
is only possible in species which have a “compact” pancreas (e.g., Anguillu
vulgaris; cf. Macleod, 1922), but then this would be pancreatectomy.