SPIROCH MTA BALBIANIL AND SPIROCHMTA ANODONTA. 23 
end. ‘This wave can be seen passing down the flexible body 
in a direction opposite to that of the forward motion of the 
organism, and a return wave 1s sometimes visible in favour- 
ably placed specimens. 
The occurrence of specimens with membranes loosely 
attached to the body, while others have membranes closely 
attached and contracted against the body (see Plate 1, figs. 
5 and 8), supports the view of transverse movements of 
contractile myonemes and the waves along the body set up 
thereby. The onward gliding movement of the Spirochetes 
is thus accounted for. Its concomitant spiral rotation is, to 
my mind, obviously due to the spiral winding of the mem- 
brane which directs the long, thread-like body torsionally, 
thus guiding its movements in a spiral or corkscrew manner. 
The membrane itself does not undulate to any great extent. 
This I very soon noticed in my’ examination of living 8. 
balbianii, and some of my friends who have seen the 
organisms alive have also remarked on this fact. 
I prefer, then, the term ‘‘ membrane” to that of “ undula- 
ting’? membrane in connection with Spirochetes, thereby 
emphasising a contrast with the “organella” of Trypano- 
somes, which truly vibrates, and may be styled correctly an 
“ undulating ”? membrane. 
The lashing movements of these Spirochetes, together 
with the curling up of the posterior or free end—especially 
marked in 8. anodontz—lI ascribe to alternate contractions 
and relaxations of the myoneme fibrils of the periplast of 
the thread-like body. 
In connection with the undulations passing down the body 
it has been mentioned already that there is a feeble return 
wave (“reaction-wave’’), sometimes quite easily discernible, 
which starts from the posteriorally directed end, and passes 
forward. Atthe moment of reversal the transversely directed 
inward impulse suddenly begins from the opposite end, which 
is the former posteriorally directed one, and this change in 
the point of application of the greatest transverse pressure 
brings about the reversal of motion. It is, as it were, that 
