4. ANALYSIS O F BACTORS INVOLVED I N SYMBIOSIS
113
to the gonads, he has reported that the damage is ‘‘ directly related
in extent to severity of infection, massive infections resulting in severe
to total destruction due to ingestion of host tissue by rediae.”
In my opinion, the most extensive and detailed study of cytopathological effects on a marine snail caused by larval trematodes is
that recently contributed by James (1965). This investigator has
studied structural and chemical changes in the hepatopancreatic cells
of Littorina saxatilis tenebrosa parasitized by five species of trematodes,
Cercaria ubiquita, C. Eittorinae rudis, C. roscovita, C. lebouri and C.
parvatrema homoeotecnum. I n addition, he has compared the changes
which occur in the host’s cells in the presence of parasites with those
that occur in uninfected but starved snails. James has reported that
starvation autolysis does take place in hepatopancreatic cells if the
number of parasites present is sufficiently large to block off the lumina
of the tubules (Fig. 17). However, if the tubules are not completely
blocked, there are still reductions in the amounts of glucose, glycogen,
glycoproteins, and lipids in the host’s cells accompanied by a compensatory increase in the number of food vacuoles in the digestive cells.
He has also noted an increase in the number of secretory cells which he
believes are sufficiently effective in removing the excretory products of
the parasites from the intertubular spaces. Thus, James is of the
opinion that damage to host cells results primarily from starvation and
not from the lytic properties of the parasites’ wastes.
In analyzing the factors which may have influenced the amount of
damage inflicted on the host’s hepatopancreatic cells, James has concluded that (1) the rate of development of the parasite in relation to the
life-span of the host and the time of initial infection, (2) the mobility of
the germinal sacs (sporocysts or rediae), and (3) the physiological
resistance of the host, are all important.
In considering the first factor, James has noted that the normal lifespan of Littorina saxatilis tenebrosa at Twr Gwylanod, off the coast of
Fxa. 11. Section of hepatopancreas of Littorina saxatilia parasitized by Cercaria
Zittorime rudis sporocysts. ( 1 ) Sporocysts compressing and blocking the tubule
lumen; (2) the tubules distal to the block undergoing starvation autolysis;
(3) tubules proximal to the block with few food storage globules, many food
vacuoles, and many secretory cells; (4) hedthy tubules, uninfected by parasites,
with many food storage globules, few food vacuoles, and few secretory cells.
(Redrawn after James, 1966.)
au. a-j, Hepatopancreatic tubules showing various stages of starvation autolysia ;
c.t., connective tissue ; di. h., healthy hepatopancreatic tubule ; di. p., hepatopancreatic tubule showing physiological effects of parasitism ; Zu., lumen of hepatopancreatic tubule ; m, sporocyst containing cercarisa ; s.c., secretory cell ; u.h.,
visceral hemocoelic space.
A.I.B.-5
8
113
to the gonads, he has reported that the damage is ‘‘ directly related
in extent to severity of infection, massive infections resulting in severe
to total destruction due to ingestion of host tissue by rediae.”
In my opinion, the most extensive and detailed study of cytopathological effects on a marine snail caused by larval trematodes is
that recently contributed by James (1965). This investigator has
studied structural and chemical changes in the hepatopancreatic cells
of Littorina saxatilis tenebrosa parasitized by five species of trematodes,
Cercaria ubiquita, C. Eittorinae rudis, C. roscovita, C. lebouri and C.
parvatrema homoeotecnum. I n addition, he has compared the changes
which occur in the host’s cells in the presence of parasites with those
that occur in uninfected but starved snails. James has reported that
starvation autolysis does take place in hepatopancreatic cells if the
number of parasites present is sufficiently large to block off the lumina
of the tubules (Fig. 17). However, if the tubules are not completely
blocked, there are still reductions in the amounts of glucose, glycogen,
glycoproteins, and lipids in the host’s cells accompanied by a compensatory increase in the number of food vacuoles in the digestive cells.
He has also noted an increase in the number of secretory cells which he
believes are sufficiently effective in removing the excretory products of
the parasites from the intertubular spaces. Thus, James is of the
opinion that damage to host cells results primarily from starvation and
not from the lytic properties of the parasites’ wastes.
In analyzing the factors which may have influenced the amount of
damage inflicted on the host’s hepatopancreatic cells, James has concluded that (1) the rate of development of the parasite in relation to the
life-span of the host and the time of initial infection, (2) the mobility of
the germinal sacs (sporocysts or rediae), and (3) the physiological
resistance of the host, are all important.
In considering the first factor, James has noted that the normal lifespan of Littorina saxatilis tenebrosa at Twr Gwylanod, off the coast of
Fxa. 11. Section of hepatopancreas of Littorina saxatilia parasitized by Cercaria
Zittorime rudis sporocysts. ( 1 ) Sporocysts compressing and blocking the tubule
lumen; (2) the tubules distal to the block undergoing starvation autolysis;
(3) tubules proximal to the block with few food storage globules, many food
vacuoles, and many secretory cells; (4) hedthy tubules, uninfected by parasites,
with many food storage globules, few food vacuoles, and few secretory cells.
(Redrawn after James, 1966.)
au. a-j, Hepatopancreatic tubules showing various stages of starvation autolysia ;
c.t., connective tissue ; di. h., healthy hepatopancreatic tubule ; di. p., hepatopancreatic tubule showing physiological effects of parasitism ; Zu., lumen of hepatopancreatic tubule ; m, sporocyst containing cercarisa ; s.c., secretory cell ; u.h.,
visceral hemocoelic space.
A.I.B.-5
8