4. ANALYSIS OF FACTORS INVOLVED IN SYMBIOSIS
119
histological sections of parasitized oysters from Maryland, Virginia,
and Texas kindly donated by both Dr S. H. Hopkins and Dr V.
Sprague. Thus the primary site of infection between B. cucuZus and
our Bucephalus sp. is different. The reason for this remains undetermined.
Parasitic castration. By comparing what is known about the primary
sites of infection by trematodes in molluscs, it is quite evident that in
the majority of cases the hepatopancreas is the preferred site. Cheng
and Cooperman (1964) have found that larval trematodes may invade
the reproductive system secondarily after completely filling the spaces
enclosed by the tunica propria of the hepatopancreas, thus confirming
the findings by F. G. Rees (1934), Cooley (1962) and Cheng and Burton
(1965a). On the other hand, apparently among certain other species
such as Himasthla leptosoma and C. lophocerca, as reported by W. J.
Rees (1936a), and Bucephakus cuculus, the gonads are the primary
sites of infection, followed by secondary invasion of the hepatopancreas
after the gonads become completely destroyed.
The invasion and destruction of the mollusc’s gonads, especially
the germinal epithelium, is commonly referred to as parasitic castration.
This aspect of molluscan host-parasite relationship is believed by some
to be of practical importance in the biological control of medically and
economically important species (Nagano, 1927 ; Brumpt, 1941 ; Bayer,
1954; Michelson, 1957).
Relative to interference with gamete formation in trematodeparasitized molluscs, gametogenesis need not be completely inhibited.
For example, Coelho (1954), Najarian (1961), Pesigan et al. (1958),
Etges and Gresso (1965), Zischke and Zischke (1965), and others have
all reported that there may be a decrease in but not necessarily complete elimination of egg production in parasitized snails. Furthermore,
the percentage of sterile eggs is greater among those produced by
parasitized snails (Coehlo, 1954 ; Zischke and Zischke, 1965 ; and others).
Complete sterilization does occur also (Pan, 1965).
Another aspect of parasitic castration which has interested biologists
has to do with gigantism. Wesenberg-Lund (1934) appears to be the
first to have reported that molluscs parasitized by larval trematodes
become abnormally large. Specifically, he found that parasitized Radix
auricularis ( = Lymnaea auriculata) become larger. He has offered
the explanation that gigantism results from excessive growth induced
by the presence of the parasites, suggesting an excessive consumption
of food to meet the demands of the parasite.
The classic observations on gigantism are those by Rothschild (1936,
119
histological sections of parasitized oysters from Maryland, Virginia,
and Texas kindly donated by both Dr S. H. Hopkins and Dr V.
Sprague. Thus the primary site of infection between B. cucuZus and
our Bucephalus sp. is different. The reason for this remains undetermined.
Parasitic castration. By comparing what is known about the primary
sites of infection by trematodes in molluscs, it is quite evident that in
the majority of cases the hepatopancreas is the preferred site. Cheng
and Cooperman (1964) have found that larval trematodes may invade
the reproductive system secondarily after completely filling the spaces
enclosed by the tunica propria of the hepatopancreas, thus confirming
the findings by F. G. Rees (1934), Cooley (1962) and Cheng and Burton
(1965a). On the other hand, apparently among certain other species
such as Himasthla leptosoma and C. lophocerca, as reported by W. J.
Rees (1936a), and Bucephakus cuculus, the gonads are the primary
sites of infection, followed by secondary invasion of the hepatopancreas
after the gonads become completely destroyed.
The invasion and destruction of the mollusc’s gonads, especially
the germinal epithelium, is commonly referred to as parasitic castration.
This aspect of molluscan host-parasite relationship is believed by some
to be of practical importance in the biological control of medically and
economically important species (Nagano, 1927 ; Brumpt, 1941 ; Bayer,
1954; Michelson, 1957).
Relative to interference with gamete formation in trematodeparasitized molluscs, gametogenesis need not be completely inhibited.
For example, Coelho (1954), Najarian (1961), Pesigan et al. (1958),
Etges and Gresso (1965), Zischke and Zischke (1965), and others have
all reported that there may be a decrease in but not necessarily complete elimination of egg production in parasitized snails. Furthermore,
the percentage of sterile eggs is greater among those produced by
parasitized snails (Coehlo, 1954 ; Zischke and Zischke, 1965 ; and others).
Complete sterilization does occur also (Pan, 1965).
Another aspect of parasitic castration which has interested biologists
has to do with gigantism. Wesenberg-Lund (1934) appears to be the
first to have reported that molluscs parasitized by larval trematodes
become abnormally large. Specifically, he found that parasitized Radix
auricularis ( = Lymnaea auriculata) become larger. He has offered
the explanation that gigantism results from excessive growth induced
by the presence of the parasites, suggesting an excessive consumption
of food to meet the demands of the parasite.
The classic observations on gigantism are those by Rothschild (1936,