4. ANALYSIS OF FACTORS INVOLVED I N SYMBIOSIS
69
encapsulation cause the death of the parasite or is the host reaction the
result of stimulation by dead or dying parasites? This question should
be tested.
Another incidence of encapsulation within Crassostrea virginica that
provides some information pertaining to its role in the destruction of
incompatible parasites has been reported by Cheng ( 1966a). Specimens
of C. virginica that had been introduced to Hawaiian waters were
examined during 1965. It was found that a relatively large number
harbored metacestodes of the lecanicephalid cestode Tylocephalum sp.
This cestode was originally described from the pearl oyster, MargaritiFIG. 13. Healthy and resorbed Tylocephalum metacestodes in Crassostrea virginica.
Notice lack of host’s cellular reaction around healthy rnetacestode ( M ) and conspicuous reaction surrounding resorbed metacestode (R). (After Cheng, 1966a.)
fera vulgaris, in Ceylonese waters. Its complete life cycle, including its
definitive host, remains unknown ; however, the ciliated coracidium
and its modes of penetration into C. virginica were reported by Cheng
(1966a). Thus in Hawaii, C. virginica, introduced from the Atlantic
seaboard of the continental United States where Tylocephalum metacestodes have only recently been reported, is believed not to be the
natural intermediate host. The cestode larvae will undergo what
appears to be normal development in C. virginica (Fig. 13), but when
it is well developed a delayed but nevertheless conspicuous encapsula-
69
encapsulation cause the death of the parasite or is the host reaction the
result of stimulation by dead or dying parasites? This question should
be tested.
Another incidence of encapsulation within Crassostrea virginica that
provides some information pertaining to its role in the destruction of
incompatible parasites has been reported by Cheng ( 1966a). Specimens
of C. virginica that had been introduced to Hawaiian waters were
examined during 1965. It was found that a relatively large number
harbored metacestodes of the lecanicephalid cestode Tylocephalum sp.
This cestode was originally described from the pearl oyster, MargaritiFIG. 13. Healthy and resorbed Tylocephalum metacestodes in Crassostrea virginica.
Notice lack of host’s cellular reaction around healthy rnetacestode ( M ) and conspicuous reaction surrounding resorbed metacestode (R). (After Cheng, 1966a.)
fera vulgaris, in Ceylonese waters. Its complete life cycle, including its
definitive host, remains unknown ; however, the ciliated coracidium
and its modes of penetration into C. virginica were reported by Cheng
(1966a). Thus in Hawaii, C. virginica, introduced from the Atlantic
seaboard of the continental United States where Tylocephalum metacestodes have only recently been reported, is believed not to be the
natural intermediate host. The cestode larvae will undergo what
appears to be normal development in C. virginica (Fig. 13), but when
it is well developed a delayed but nevertheless conspicuous encapsula-