SPIROCH JETES : LIFE-CYCLE 73 



and sometimes the spirochsete seems to roll itself 

 up into a ball. Further, the ball may be central 

 or terminal, or in any position between the two. 

 Usually, if watched long enough, the ball unrolls 

 again and the organism swims away unchanged. If 

 stained preparations only be examined, the con- 

 clusion is that these balls are veritable cysts, and 

 that the spirochsetes have produced a resting form. 

 Such a resting stage is, however, still problematic in 

 the case of nearly all spirochaetes. 



Not only have the modes of division and move- 

 ments of spirochsetes been studied in the larger 

 spirochsetes of Lamellibranchs, but we have also 

 minutely examined the smaller ones parasitic in the 

 blood of mammals and birds and in the alimentary 

 tracts of certain insects. There is a remarkable 

 similarity between the structure and movements of 

 these blood-dwellers and of those spirochsetes in- 

 habiting the crystalline styles of molluscs. Further, 

 the life-cycles of all the spirochsetes fully investigated 

 are on the same lines. It would, perhaps, be as well 

 to complete the life-cycle of the molluscan spirochsete, 

 for this cycle usually needs one host for its accom- 

 plishment, whereas the blood-spirochsete often under- 

 goes one stage of its development in a second host. 



Spirochata balbianii of oysters, Tapes, and other 

 molluscs, S. anodonta, S. mityli, and also S. solenis, 

 have been under observation by us for some years. 

 During this time, small, ovoid bodies (" spores ") of 

 the same diameter as spirochsetes have been found 

 from time to time, and also empty sheaths in both 

 the crystalline style, the alimentary tract, the in- 



