H. B. Fantham 
395 
away. Parasites fixed in the coiled position and then stained (PI. VI, 
Fig. 53) suggest encystment. Study of the living organism shows that 
true encystment does not occur. 
Agglutination was not seen in the Spirochaetes of Tapes aureus. 
General Morphology. 
The structure of the Spirochaetes of various Lamellibranchs has 
been more or less fully described by Laveran and Mesnil (1901), Perrin 
(1906), Keysselitz (1906—7), Swellengrebel (1907), Fantham (1907—8), 
Gonder (1908), Schellack (1909) and others. I made a detailed study 
of two such Spirochaetes S. balbianii and S. anodontae in 1906—7. It 
will not be necessary to repeat in detail an account of the typical 
structure of a Spirochaete as seen in specimens from the gut of Tapes 
aureus. A summary of the leading features will suffice. 
A Spirochaete is covered externally by a flexible periplast, which, 
when stained under favourable conditions, shows contractile threads or 
myonemes (Text-fig. 1). Miss Porter (1909), using dark-ground 
illumination, has actually seen pulsations travelling along the myonetne 
fibrils in living S. anodontae. Internal to the periplast is the nuclear 
apparatus, which during the trophic phase consists of transverse bars 
of chromatin, as judged by staining reactions. These chromatin bars 
Text-fig. 1. Diagram of a typical Spirochaete (e.g. S. balbianii) with rounded ends, 
from marine Lamellibranchs. 
b.g. = basal granule. 
chr. — transverse bar of chromatin. 
membr. — membrane with myonemes (my.) approximately longitudinally disposed. 
are really joined obliquely by achromatic connections (PI. VI, Fig. 39) 
—usually better seen during division. The whole nuclear system forms 
a somewhat flattened helix, the turns of which closely approximate to 
the external periplast. During division the chromatin is somewhat 
rearranged, for some stainable granules (presumably of chromatin) 
migrate into the more achromatic, oblique portions of the spiral, and 
so the helix is more easily stained as a whole. 
The rest of the substance of the body of a Spirochaete seems to 
be of a cytoplasmic nature, possibly somewhat alveolar. As I have 
