66 SOME MINUTE ANIMAL PARASITES 



genus of organisms. Concurrently, one of us had 

 been studying not only the spirochaete of oysters, 

 but also a new species of spirochaete discovered by 

 us in the British fresh-water mussel, Anodontacygnea, 

 and the results of this work were published in 1907- 

 1908, with an extension in 1909. Other spirochaetes 

 from sea-mussels, Tapes, Solen, Sphaerium, sheep- 

 keds, bees, wasps, grouse, fowls, monkeys, and man 

 and other animals, have since been recorded and 

 described by us. Naturally the greatest amount of 

 detail can be obtained from the structure of a 

 relatively large spirochaete, such as that from the 

 oyster, and much valuable information can be 

 obtained from it. Nevertheless the same structures 

 on a far smaller scale and hence with less definite- 

 ness can be observed in most of the smaller spiro- 

 chaetes, such as those inhabiting the blood of 

 mammals and birds. 



The study of spirochaetes is well commenced, then, 

 with those found in the crystalline style and diges- 

 tive tract of the edible " shellfish," oysters, sea and 

 fresh-water mussels, and Tapes, the latter being 

 in common use for food on the coasts of the 

 Mediterranean. 



The body of any spirochaete is a long, slender 

 structure (Fig. 18) which twists spirally on itself, 

 and is capable of rapid extension and contraction. 

 The number of coils is not fixed. The sinuous body 

 extends outwards as a spirally wound protrusion 

 forming a " fin " or flange called a membrane 

 (Fig. 18, c), the winding being much like that of 

 the thread of a screw. This membrane serves to 



