72 SOME MINUTE ANIMAL PARASITES 



same spot repeatedly. Their course is usually a 

 straight one. When movement is very rapid, the 

 membrane is drawn nearer to the body to lessen the 

 resistance to the medium in which the organism is 

 placed. Slow-moving spirochsetes show wider that 

 is, relaxed membranes. 



Simple looping movements are common. The 

 parasites bend on themselves, form loops like U, 

 and each arm alternately is raised and lowered. A 

 variation of this is seen when the two arms of the 

 U intertwine, and the two ends only are free. This 

 phenomenon has been seen in thousands of speci- 

 mens, but the results of our own observations have 

 been that the spirochaetes finally disentangled them- 

 selves and swam away. Other observers say that 

 transverse division occurs at the bend, and consider 

 that this peculiar bending has been mistaken for 

 longitudinal division. This is not so. In longi- 

 tudinal division one body is seen at one period, and 

 there is the succession of nuclear changes, the 

 doubling of the membrane, and until the final separa- 

 tion occurs, one thick parental body with two thinner 

 daughter ones originating from it. Such a body 

 arrangement is never seen in entanglement pheno- 

 mena. 



Again, spirochsetes use a sort of boring movement, 

 and spirally bore their way upwards through the 

 medium surrounding them. Their appearance as 

 they advance obliquely towards the surface is that 

 of an animated Catherine wheel rotating violently on 

 itself. 



Watchspring-like coilings and uncoilings occur, 



