6 H. B. FANTHAM. 
polymorphism occurs; while the precise method or methods 
of division also require re-investigation. I hope to deal with 
these questions in the sequel, but the Spirochetes—on 
account of their minute size and active movements—offer 
the very greatest difficulties as objects of research, and, in ~ 
endeavouring to elucidate some of these difficulties, one must 
try to preserve an open mind, and not be dogmatic. 
Regarding Spirocheta anodonte, as stated already, 
this form was discovered and briefly described by Keysselitz 
(4) in 1906 in the crystalline style of Anodonta mutabilis. 
Its occurrence in the British mussel, A. cygnea, was not 
recorded previously to my note before the Zoological Society. 
I hope in the following to set forth some details regarding 
its movements and morphology. | 
MATERIAL AND THE OCCURRENCE OF PARASITES THEREIN. 
I think it would be well to treat together of the material 
used and the occurrence of the parasites therein, and not to 
take these sections separately as was at first intended. 
Oysters and fresh-water mussels are common enough, but 
infected specimens are not by any means plentiful in either 
case. ‘The material for the study of Spirocheta balbianit 
was obtained alive in Roscoff from oysters imported from 
Abervrach, and later in London from Hnglish native oysters. 
Many samples of English oysters were tried, for example, 
from Whitstable direct, Brightlingsea, Shoreham, and other 
places, sometimes unknown. The infected specimens were 
bought at Billingsgate, and were stated to be English natives, 
but that was all the information vouchsafed, though others 
can be got from the same bed. There have been several 
“‘ oyster scares” lately, and dealers are somewhat reticent. 
The infected oysters were rather small and came from very 
muddy beds, and all who saw them remarked that they did 
not look very palatable. The oysters were kept alive in sea 
water for the space of a fortnight. This water was constantly 
changed, and was sometimes previously filtered. 
With regard to Spirochetes in oysters there is a great 
