266 DR. ZENKER, ON INFUSORIA. 
time by a thin covering class, without being destroyed. In 
them also it may be seen that a number (5—8) of serpen- 
tine canals radiate from the pulsating vesicle, the gra- 
dually finer and finer branches of which canals may be traced 
over both sides of the surface of the body. These canals 
were regarded by Wiegmann, and afterwards by Von Siebold, 
as the conduits of an oscillating, blood-circulation, be- 
cause they observed them to become distended with fluid im- 
mediately after the systole of the vesicle itself. And this 
phenomenon, it must be confessed, very readily led to the 
impression that the wovement of the fluid was from the 
vesicle towards the canals. 
Nevertheless, if a Bursaria leucas be laid upon its side, in 
such a position that the pulsating vesicle is viewed at its 
greatest distance from the axis of the body, it will be plainly 
seen to he immediately beneath the outer membrane, and that 
at each systole it contracts In an outward direction. And the 
same condition, with fewer exceptions, as, for instance, in 
the Vorticellz, obtains in all other Infusoria. But in no case 
can the contained fluid be seen to retire towards the interior 
of the body ; we are compelled, therefore, to assume the ex- 
istence of an external orifice. 
This orifice becomes visible when the animal is so turned 
that the vesicle appears to le in the axis of the body, and 
consequently when it is in a position to be looked into either 
from the outer or the imner aspect. Under these circum- 
stances, there will be seen in the centre of the spherical 
vesicle a smaller circle, with sharply defined borders, which 
are best seen in oblique illumination, the circlet itself pre- 
senting a bluish-grey colour. Thus it remains during the 
whole diastole ; at the moment of the completion of which its 
colour suddenly changes into the same palish-red hue as the 
rest of the vesicle; and from this moment the vesicle col- 
lapses. 
The orifice consequently in this case is constantly existent: 
but by careful adjustment of the microscope an extremely 
delicate viscous substance will be perceived by which the 
orifice during the diastole is covered, and, as it were, plastered 
over. I have often witnessed the rupture of this substance com- 
mencing on each side, before the collapse of the vesicle, and the 
assumption of the red colour by the orifice. 
The presence of this cement renders the simple nature of 
the proceeding perfectly clear, During the diastole the flow 
of fluid brought by the vessels compresses the surrounding 
substance uniformly in every direction. The further the 
