146
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Description. Body usually broad and fan-shaped, with large clear
ectoplasmic pseudopodium a t forward moving end ; posterior end commonly pointed, usually with small fine pseudopodia extending from it ;
specimens taken from plate culture during initial 3-4 days are more or
less uniform in size, measuring 21 p long x 13 p wide, after that many
small amoebae, resulting from division and measuring 1-6 p in greater
diameter, are present in addition to giant multinucleated forms which
may be as large as 143.3 p in greatest diameter ; ecto- and endoplasms
distinct ; with small dense and large refractile granules in endoplasm ;
small granules may enter ectoplasm in moribund specimens but large
ones are limited to endoplasm ; no contractile vacuoles present ; some
food vacuoles, filled with bacteria and other finely granular materials,
present ; nucleus generally spherical, with large slightly eccentric
karyosome; large and small chromatin granules on inner surface of
nuclear membrane ; reproduction by binary fission and exogenous and
endogenous budding. Cyst spherical, thin, transparent and with
regular outline ; believed to be semipermeable ; varies greatly in size,
those found on surface of agar cultures measure 11-1 8 p in diameter,
those found in hanging-drop cultures measure 4-12 p in diameter ;
single nucleus present ; cytoplasm with one or more vacuoles.
Life cycle. The life cycle of 8. patuxent is only known from laboratory
observations on cultures (Hogue, 1921). Trophozoites reproduce by
binary fission and by budding, both exogenously and endogenously.
Occasionally encystment occurs but excystment has not been observed.
How oysters become infected is not known although presumably cysts,
and even trophozoites, if the latter is ever free-living, could be ingested.
Ecology. Hogue (1921) has studied the influence of the environment
on cultures of V . patuxent. Earlier (Hogue, 1917) she had demonstrated
that the density of the culture medium influences the shape of amoebae.
This was confirmed in 1921. If V . patuxent is cultured on agar to which
no moisture is added, the amoebae group together and even overlap.
When a 0.7% NaCl solution is added to the agar surface, the amoebae
move about freely and those a t the edge become greatly elongated (Fig.
27). Hogue has proposed that the reason for this is the one given earlier
by Uhlenhuth (1915) who claimed it is I ‘ due to the fact that the desired
relation between the consistency of the medium and the consistency of
the cell plasma has been reached resulting in greater freedom of movement.”
Hogue also has demonstrated that if amoebae are contained in a
drop of agar medium contaminated with moulds, they immediately
stretch out along the fungal hyphae if contact is made (Fig. 28).
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Description. Body usually broad and fan-shaped, with large clear
ectoplasmic pseudopodium a t forward moving end ; posterior end commonly pointed, usually with small fine pseudopodia extending from it ;
specimens taken from plate culture during initial 3-4 days are more or
less uniform in size, measuring 21 p long x 13 p wide, after that many
small amoebae, resulting from division and measuring 1-6 p in greater
diameter, are present in addition to giant multinucleated forms which
may be as large as 143.3 p in greatest diameter ; ecto- and endoplasms
distinct ; with small dense and large refractile granules in endoplasm ;
small granules may enter ectoplasm in moribund specimens but large
ones are limited to endoplasm ; no contractile vacuoles present ; some
food vacuoles, filled with bacteria and other finely granular materials,
present ; nucleus generally spherical, with large slightly eccentric
karyosome; large and small chromatin granules on inner surface of
nuclear membrane ; reproduction by binary fission and exogenous and
endogenous budding. Cyst spherical, thin, transparent and with
regular outline ; believed to be semipermeable ; varies greatly in size,
those found on surface of agar cultures measure 11-1 8 p in diameter,
those found in hanging-drop cultures measure 4-12 p in diameter ;
single nucleus present ; cytoplasm with one or more vacuoles.
Life cycle. The life cycle of 8. patuxent is only known from laboratory
observations on cultures (Hogue, 1921). Trophozoites reproduce by
binary fission and by budding, both exogenously and endogenously.
Occasionally encystment occurs but excystment has not been observed.
How oysters become infected is not known although presumably cysts,
and even trophozoites, if the latter is ever free-living, could be ingested.
Ecology. Hogue (1921) has studied the influence of the environment
on cultures of V . patuxent. Earlier (Hogue, 1917) she had demonstrated
that the density of the culture medium influences the shape of amoebae.
This was confirmed in 1921. If V . patuxent is cultured on agar to which
no moisture is added, the amoebae group together and even overlap.
When a 0.7% NaCl solution is added to the agar surface, the amoebae
move about freely and those a t the edge become greatly elongated (Fig.
27). Hogue has proposed that the reason for this is the one given earlier
by Uhlenhuth (1915) who claimed it is I ‘ due to the fact that the desired
relation between the consistency of the medium and the consistency of
the cell plasma has been reached resulting in greater freedom of movement.”
Hogue also has demonstrated that if amoebae are contained in a
drop of agar medium contaminated with moulds, they immediately
stretch out along the fungal hyphae if contact is made (Fig. 28).