70 SOME MINUTE ANIMAL PARASITES 



here. Also the protoplasm tends to pass from this 

 region of the organism to a great extent. When the 

 strain due to the succession of wave-pulls becomes 

 too great, the spirochsete parts in two, and the 

 elastic outer layer of the body the periplast 

 closes over the separated ends. 

 The two daughter organisms 

 thus produced usually swim 

 away in opposite directions. 



There is an enormous varia- 

 tion in the size and appearance 

 of the spirochaetes found in 

 any one mollusc, but practi- 

 cally all the differences can be 

 explained by reference to the 

 modes of division, followed by 

 subsequent growth. When 

 longitudinal division occurs 

 rapidly as it often does then 

 a multiplicity of forms of all 

 grades of thickness is found 

 FP (Fig- 19)- When, on the other 



hand, transverse division has 

 FIG. i Q MORPHOLOGICAL , r ,. . 



VARIATION IN THE been frequent, the spirochaetes 



SPIROCH/ETE FROM pres ent greater variations so 



TAPES AUREUS 



far as length is concerned. 



Longitudinal division, followed so rapidly by trans- 

 verse division that the products of the first fission 

 had not effected their final separation, has been 

 observed in certain of the spirochaetes of molluscs. 

 On the other hand, this last phenomenon has not 

 been seen in the blood-spirochaetes, but there appears 



