4. AXALYSIS O F FACTORS INVOLVED I N SYMBIOSIS
95
has not been recorded in any protozoa, mesozoa, helminth or, to my
knowledge, arthropod. It has been found in the conjugated bile acids
of mammals as taurocholic acid, and in other tissues as well, having
been metabolized from cysteine, usually via cysteine sulfenic acid -+
cysteine sulfinic acid -+ cysteic acid -+ taurine, although alternate
pathways may occur.
4. Digestive enzymes
Nothing is known at this time about the role of digestive enzymes of
molluscs in the biology of parasites and mutualists. From the reviews of
digestion in molluscs, primarily pelecypods and gastropods, presented
by Galtsoff (1964), van Wee1 (1961) and Reid (1966), it would appear
that considerably more needs to be learned about the nature and function of digestive enzymes in molluscs.
5. Control of maturation
Again, nothing is known at this time as to what host factors may be
involved in the control of maturation of parasites and mutualists of
molluscs other than the possible role of sex hormones on larval trematodes (Szidat, 1959). With our increasing knowledge concerning hormones and neurosecretions in molluscs (Charniaux-Cotton and Kleinholz, 1964; Simpson et al., 1966), it may be possible in the not too
distant future that the influence of hosts’ hormones on the maturation
of parasites and mutualists will be explored.
6. Resultant pathology
I n the past, prior to the advent of a physiological or biochemical
approach to understanding host-symbiont relationships, that aspect of
symbiosis known as parasitism was often defined as a relationship
during which the parasite inflicts some injury to its host. Although this
definition has now been rejected, it still remains true, nevertheless, that
parasites, in varying degrees, do very often inflict “ injury ” to their
hosts. “ Injury,” unfortunately, is a difficult term to define without
involving anthropocentric judgmenh. It is primarily for this reason
that the older definition of parasitism is being rejected. On the other
hand, pathological change, especially histopathological manifestations,
expressed from a functional viewpoint, can be a rewarding and fruitful
avenue of research. A certain number of studies of this nature have been
made on marine molluscs in connection with parasitism, and these are
reviewed below.
I n considering parasite-caused pathology, it should be emphasized
that evaluation of the lethality of such changes must be approached
95
has not been recorded in any protozoa, mesozoa, helminth or, to my
knowledge, arthropod. It has been found in the conjugated bile acids
of mammals as taurocholic acid, and in other tissues as well, having
been metabolized from cysteine, usually via cysteine sulfenic acid -+
cysteine sulfinic acid -+ cysteic acid -+ taurine, although alternate
pathways may occur.
4. Digestive enzymes
Nothing is known at this time about the role of digestive enzymes of
molluscs in the biology of parasites and mutualists. From the reviews of
digestion in molluscs, primarily pelecypods and gastropods, presented
by Galtsoff (1964), van Wee1 (1961) and Reid (1966), it would appear
that considerably more needs to be learned about the nature and function of digestive enzymes in molluscs.
5. Control of maturation
Again, nothing is known at this time as to what host factors may be
involved in the control of maturation of parasites and mutualists of
molluscs other than the possible role of sex hormones on larval trematodes (Szidat, 1959). With our increasing knowledge concerning hormones and neurosecretions in molluscs (Charniaux-Cotton and Kleinholz, 1964; Simpson et al., 1966), it may be possible in the not too
distant future that the influence of hosts’ hormones on the maturation
of parasites and mutualists will be explored.
6. Resultant pathology
I n the past, prior to the advent of a physiological or biochemical
approach to understanding host-symbiont relationships, that aspect of
symbiosis known as parasitism was often defined as a relationship
during which the parasite inflicts some injury to its host. Although this
definition has now been rejected, it still remains true, nevertheless, that
parasites, in varying degrees, do very often inflict “ injury ” to their
hosts. “ Injury,” unfortunately, is a difficult term to define without
involving anthropocentric judgmenh. It is primarily for this reason
that the older definition of parasitism is being rejected. On the other
hand, pathological change, especially histopathological manifestations,
expressed from a functional viewpoint, can be a rewarding and fruitful
avenue of research. A certain number of studies of this nature have been
made on marine molluscs in connection with parasitism, and these are
reviewed below.
I n considering parasite-caused pathology, it should be emphasized
that evaluation of the lethality of such changes must be approached