20 SPIROCILETES. 



that these appendages are formed in the process of 

 division of the spirochaste, and thus may not be per- 

 manent. Perrin speaks of the periplast retaining its 

 form after the entoplasm has escaped from within it 

 and become 'encysted. 



Attached to the periplast or forming part of it is the 

 so-called undulating membrane (Figs. 2, 3). This is 

 described as running round the body of the spirochaete 

 in a spiral direction, and as being bounded at its external 

 margin by a darkly staining fibril (randfibrille) , while 

 other fibrils may be seen running in it parallel to the 

 marginal one. The latter is said to be connected at its 

 extremities with two darkly staining particles, situated 

 at the ends of the spirochaete, called by Gonder bleph- 

 aroplasts, on the analogy of the blepharoplast of 

 trypanosomes. 



The nature of this undulating membrane has been 

 called in question. Laveran and Mesnil regard the 

 appearance thus named as produced by the existence 

 of a loose sheath outside the spirochaste ; and a sheath 

 has been described in several of the smaller spiro- 

 chaetes by different writers (see p. 26). Schellack 

 believes that the so-called undulating membrane is an 

 artifact, produced in the process of fixation. My own ex- 

 perience with Sp. anodontcs would seem to support this 

 view, as I find that the better the specimen is fixed, the 

 less frequent are individuals which appear to have 

 undulating membranes. Nor does the appearance 

 when present correspond at all closely with that seen 

 in trypanosomes, the marginal fibril being often seen 

 as a separate structure with no membrane visible 

 between it and the body of the spirochaete, and often 

 also appearing at only one or two points, not as a struc- 

 ture continuous all along the organism. The appear- 



