4. ANALYSIS OF FACTORS INVOLVED I N SYMBIOSIS
73
and encapsulation, can only be brought about with a clearer understanding of these aspects of molluscan hematology.
d. Nacrezation
This is a new term which is being coined to describe a type of
molluscan defense mechanism which does not subscribe to any of the
foregoing categories. Nacrezation involves a series of processes which
result in the walling off of foreign materials by a layer or layers of
nacre, thus forming a pearl. This type of defense mechanism against
zooparasites has been known since the report of Worm in 1655 that
pearly formations occur in the mantle of Mytilus edulis collected in
Sweden. This original observation was followed by the studies of
Dubois (1901, 1907), Jameson (1902), Giard (1907), and others. It is
now known that certain trematode metacercariae, especially those of
Gymnophallus margaritarum, that are found between the shell and
mantle of marine pelecypods, will stimulate the mantle to secrete
nacre which becomes deposited around the parasites.
Nacrezation is not limited to protection against trematode larvae.
It has long been known that polychaetes of the genus Polydora,
commonly referred to as mud blister worms, are prevented from reaching the soft tissues of oysters by the laying down of nacre by the
underlying mantle epithelium as soon as the annelids break through
the internal shell surface.
e. Humoral immunity
Most, if not all, of our information on the existence of humoral
immunity in molluscs is based on indirect evidences. For simplicity
in presentation, evidence for the occurrence of humoral immunity in
molluscs is being classified as natural (innate) and acquired.
Natural factors. The earlier literature pertaining to naturally
occurring humoral factors is difficult to analyze critically since the
molluscs studied were all caught in the wild, hence their histories were
not available. Couvreur (1923) has reported the occurrence of a natural
antitoxin in Helixpomatia. Chahovitch (1921) has reported the presence
of a natural hemagglutinin in the cephalopod Sepia. More recently,
Tyler (1946) has reported natural agglutinating activity when the blood
cells and spermatozoa of a number of non-molluscan invertebrates were
placed in the body fluids of five marine gastropods, Acmea digitalis,
Lattia gigantia, Tegula galena, Astraea undosa and Megathura crenulata,
and one pelecypod, Mytilus californianus. I n no instance did the fluids
affect blood cells or spermatozoa of animals of the same taxonomic class,
73
and encapsulation, can only be brought about with a clearer understanding of these aspects of molluscan hematology.
d. Nacrezation
This is a new term which is being coined to describe a type of
molluscan defense mechanism which does not subscribe to any of the
foregoing categories. Nacrezation involves a series of processes which
result in the walling off of foreign materials by a layer or layers of
nacre, thus forming a pearl. This type of defense mechanism against
zooparasites has been known since the report of Worm in 1655 that
pearly formations occur in the mantle of Mytilus edulis collected in
Sweden. This original observation was followed by the studies of
Dubois (1901, 1907), Jameson (1902), Giard (1907), and others. It is
now known that certain trematode metacercariae, especially those of
Gymnophallus margaritarum, that are found between the shell and
mantle of marine pelecypods, will stimulate the mantle to secrete
nacre which becomes deposited around the parasites.
Nacrezation is not limited to protection against trematode larvae.
It has long been known that polychaetes of the genus Polydora,
commonly referred to as mud blister worms, are prevented from reaching the soft tissues of oysters by the laying down of nacre by the
underlying mantle epithelium as soon as the annelids break through
the internal shell surface.
e. Humoral immunity
Most, if not all, of our information on the existence of humoral
immunity in molluscs is based on indirect evidences. For simplicity
in presentation, evidence for the occurrence of humoral immunity in
molluscs is being classified as natural (innate) and acquired.
Natural factors. The earlier literature pertaining to naturally
occurring humoral factors is difficult to analyze critically since the
molluscs studied were all caught in the wild, hence their histories were
not available. Couvreur (1923) has reported the occurrence of a natural
antitoxin in Helixpomatia. Chahovitch (1921) has reported the presence
of a natural hemagglutinin in the cephalopod Sepia. More recently,
Tyler (1946) has reported natural agglutinating activity when the blood
cells and spermatozoa of a number of non-molluscan invertebrates were
placed in the body fluids of five marine gastropods, Acmea digitalis,
Lattia gigantia, Tegula galena, Astraea undosa and Megathura crenulata,
and one pelecypod, Mytilus californianus. I n no instance did the fluids
affect blood cells or spermatozoa of animals of the same taxonomic class,