SPIROCHETA BALBIANIL AND SPIROCHETA ANODONTA. 20 
ment in these cases is amplified into the abnormal or 
nearly so. 
Perrin considers that the membrane is only of secondary 
importance in the mechanism of movement, for he states that 
“there is but- little noticeable difference in the motion of 
forms with or without it.” Now there is probably no form of 
S. balbianii (or S. anodonte) devoid of a membrane, and 
in those organisms apparently without it the structure is 
really present and closely contracted round the body, as 
shown by its deeply staining border being seen as a sinuous 
line along the outside of the periplast in all such when 
successfully stained (vide Pl. 1, figs. 4, 7; Pl. 2, fig. 
34; also Pl. 3, fig. 23). 
It might, perhaps, be urged by the hypercritical that the 
undulations seen passing along the body in motion are only 
“optical illusions” due to the organism turning round on 
itself, and so bringing different points of the body into focus 
under the microscope. I do not think so myself. I hope I 
have shown, in this section of the memoir, the necessity for 
the presence of these waves in aiding in the motion of the 
organism. Also, in carefully fixed and stained preparations, 
the body is actually seen fixed in the form of waves, as a 
sinuous thread; in fact, rigid and straight forms of Spiro- 
_ chetes are hardly ever encountered, for such, if persistent, 
would belong more properly to the genus Spirillum. Opti- 
eal illusions cannot be stained so as to show when illuminated 
by a wide-angled central pencil of light. 
The central nuclear thread is, I think, merely flexible, that 
is, able to be bent into the form of the waves set up by the 
myonemes. I do not consider the nuclear thread to be 
contractile (other than possessing the general “tonic con- 
tractility ” in common with all forms of protoplasm), as ‘is, 
perhaps, suggested by Swellengrebel (10). But really he 
may mean the chromatin border of the membrane, which 
certainly is contractile—his context is a little vague on this 
matter. 
