106
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
tissues will gradually recover, undergo regeneration, and finally become
normal. Cort (1941) has stated that the recovery from a trematode
infection would have to involve the walling off of old sporocysts and
rediae and the regeneration of tissues. He has commented that in all
his examinations of snails infected with trematode larvae, he has never
seen one suggesting recovery from an old infection. Not enough is
known about environmental and physiological conditions which favor
or inhibit the loss of infections in molluscs to warrant evaluation of
these seemingly opposed viewpoints. It should be pointed out, however, that molluscs can lose their trematode infections (Standen, 1963 ;
Kendall, 1964)) especially if maintained a t less than optimum conditions, such as at lower temperatures (Stirewalt, 1954).
From the speculative viewpoint, there is no reason to believe that
molluscs are not capable of wound healing. I n Crassostrea virginica,
Mackin (1961) has suggested, although experimental proof has not
been provided, that epithelial encapsulation of injured tissues could
occur and the entire lesion may be discharged through the external
epithelium. Pauley and Sparks (1965) have contributed a study of
acute inflammatory reactions in the Pacific oyster, C. gigas. Although
their experiments were not carried out long enough after injection of
turpentine into the tissues to suggest wound healing, in their discussion
they suggested that healing may occur by " (1) fibrous encapsulation
of the injury and eventually fibrous infiltration of the wound to form
a scar ; (2) the normal Leydig cells surrounding the injured area will
grow together once the injurious substance is removed;" and (3) the
epithelial encapsulation and discharge process suggested by Mackin
discussed earlier. Pauley and Sparks (1966) have given a more detailed
account of this and similar experiments in a more recent paper in
which they pointed out the importance of amoebocytes in inflammatory
reactions.
In the preceding paragraphs, pathological changes in molluscs in
general caused by essentially intercellular parasites have been reviewed.
Several of the contributors cited worked with marine molluscs. Their
results are given further detailed consideration at this point.
F. G. Rees (1934) has studied pathological changes in the marine
gastropod Patella vulgata parasitized by the rediae of Cercaria patellae.
She has demonstrated that the presence of rediae in the intertubular
spaces within the hepatopancreas results in profound damage, involving
local histolysis of the glandular epithelium. This is brought about by
the following set of circumstances.
The rediae, according to F. G. Rees, most probably reach the
digestive gland via the blood-stream. While lodged between the hepato-
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
tissues will gradually recover, undergo regeneration, and finally become
normal. Cort (1941) has stated that the recovery from a trematode
infection would have to involve the walling off of old sporocysts and
rediae and the regeneration of tissues. He has commented that in all
his examinations of snails infected with trematode larvae, he has never
seen one suggesting recovery from an old infection. Not enough is
known about environmental and physiological conditions which favor
or inhibit the loss of infections in molluscs to warrant evaluation of
these seemingly opposed viewpoints. It should be pointed out, however, that molluscs can lose their trematode infections (Standen, 1963 ;
Kendall, 1964)) especially if maintained a t less than optimum conditions, such as at lower temperatures (Stirewalt, 1954).
From the speculative viewpoint, there is no reason to believe that
molluscs are not capable of wound healing. I n Crassostrea virginica,
Mackin (1961) has suggested, although experimental proof has not
been provided, that epithelial encapsulation of injured tissues could
occur and the entire lesion may be discharged through the external
epithelium. Pauley and Sparks (1965) have contributed a study of
acute inflammatory reactions in the Pacific oyster, C. gigas. Although
their experiments were not carried out long enough after injection of
turpentine into the tissues to suggest wound healing, in their discussion
they suggested that healing may occur by " (1) fibrous encapsulation
of the injury and eventually fibrous infiltration of the wound to form
a scar ; (2) the normal Leydig cells surrounding the injured area will
grow together once the injurious substance is removed;" and (3) the
epithelial encapsulation and discharge process suggested by Mackin
discussed earlier. Pauley and Sparks (1966) have given a more detailed
account of this and similar experiments in a more recent paper in
which they pointed out the importance of amoebocytes in inflammatory
reactions.
In the preceding paragraphs, pathological changes in molluscs in
general caused by essentially intercellular parasites have been reviewed.
Several of the contributors cited worked with marine molluscs. Their
results are given further detailed consideration at this point.
F. G. Rees (1934) has studied pathological changes in the marine
gastropod Patella vulgata parasitized by the rediae of Cercaria patellae.
She has demonstrated that the presence of rediae in the intertubular
spaces within the hepatopancreas results in profound damage, involving
local histolysis of the glandular epithelium. This is brought about by
the following set of circumstances.
The rediae, according to F. G. Rees, most probably reach the
digestive gland via the blood-stream. While lodged between the hepato-