136
WERNER BERGMANN
verinus, which grew on this diet. Since these beetles require cholesterol
or 7-dehydrocholesterol it follows that the larvae of the flies had eliminated the supernumerary carbon atoms at C-24 of the plant sterols and
had converted them into sterols capable of sustaining the growth of
Dermes larvae.
VIII. Sterols of Mollusks
Sterol mixtures have been isolated from a comparatively large number of mollusks. Although they are in most instances rather complex
and have resisted attempts to separate them into their components,
they have nevertheless furnished adequate physical data to point toward
an interesting relation between the sterols of mollusks and their taxonomy. The significance of these relations is exceeded only by those
found for the Echinodermata. The data on mollusk sterols so far available have been summarized in Table VII.
The class of the Amphineura is of particular interest. These chitons
and related forms had been placed among the worms, Annelida, prior
to 1881 when Spengel placed them among the Mollusca. Since then
they have been thought to occupy a key position in this phylum and to
be but slightly differentiated from the prototype mollusk. It has been
shown independently and convincingly both in the United States (132)
and Japan (133, 134) that these primitive mollusks contain A
7 -sterols
(III), among which A
7 -cholestenol (III, R = A) appears to be the
principal component. This fact sets the Amphineura, or at least species
from the subclass of Polyplacophora apart from all other classes of
mollusks which have been found to contain A
5 -sterols (see Table VII).
Inclusion of data on the sterols of species from the subclass of Aplacophora, however, will be necessary before a biochemical evaluation of
the peculiar position of the Amphineura in the phylum of Mollusca
may be attempted. Most welcome will be data on the sterols of Neopilina gdlathea. This very important mollusk, which was only recently
discovered, is a "living fossil," the only known survivor of the class of
Monoplacophora.
It is also unfortunate that nothing is known about the sterols of
mollusks from the class of Scaphopoda, which were once believed to
occupy a position between the snails and the bivalves. They are held to
be very primitive mollusks, and so aberrant in structure as to warrant a
class for themselves.
All sterol mixtures which have been isolated from Gastropoda, the
snails and slugs, are rather levorotatory, indicative of the predominant
presence of A
5 -sterols. An adequate number of species from the subclass Prosobranchia and its orders Archeogastropoda, Mesogastropoda,
WERNER BERGMANN
verinus, which grew on this diet. Since these beetles require cholesterol
or 7-dehydrocholesterol it follows that the larvae of the flies had eliminated the supernumerary carbon atoms at C-24 of the plant sterols and
had converted them into sterols capable of sustaining the growth of
Dermes larvae.
VIII. Sterols of Mollusks
Sterol mixtures have been isolated from a comparatively large number of mollusks. Although they are in most instances rather complex
and have resisted attempts to separate them into their components,
they have nevertheless furnished adequate physical data to point toward
an interesting relation between the sterols of mollusks and their taxonomy. The significance of these relations is exceeded only by those
found for the Echinodermata. The data on mollusk sterols so far available have been summarized in Table VII.
The class of the Amphineura is of particular interest. These chitons
and related forms had been placed among the worms, Annelida, prior
to 1881 when Spengel placed them among the Mollusca. Since then
they have been thought to occupy a key position in this phylum and to
be but slightly differentiated from the prototype mollusk. It has been
shown independently and convincingly both in the United States (132)
and Japan (133, 134) that these primitive mollusks contain A
7 -sterols
(III), among which A
7 -cholestenol (III, R = A) appears to be the
principal component. This fact sets the Amphineura, or at least species
from the subclass of Polyplacophora apart from all other classes of
mollusks which have been found to contain A
5 -sterols (see Table VII).
Inclusion of data on the sterols of species from the subclass of Aplacophora, however, will be necessary before a biochemical evaluation of
the peculiar position of the Amphineura in the phylum of Mollusca
may be attempted. Most welcome will be data on the sterols of Neopilina gdlathea. This very important mollusk, which was only recently
discovered, is a "living fossil," the only known survivor of the class of
Monoplacophora.
It is also unfortunate that nothing is known about the sterols of
mollusks from the class of Scaphopoda, which were once believed to
occupy a position between the snails and the bivalves. They are held to
be very primitive mollusks, and so aberrant in structure as to warrant a
class for themselves.
All sterol mixtures which have been isolated from Gastropoda, the
snails and slugs, are rather levorotatory, indicative of the predominant
presence of A
5 -sterols. An adequate number of species from the subclass Prosobranchia and its orders Archeogastropoda, Mesogastropoda,