Physiology of Trichodina pediculus. 415 
seen when in place, especially where it projects beyond the tip of 
the hook, and forms with the others a succession of scallops 
(fig. 17, &) lying in a circle parallel with the margin (/') of the 
striated membrane. 
Immediately within the row of hooks a series of nazl-shaped 
pieces (i, 2”) extends im a circle, and they are arranged in such 
order that each one lies opposite the horizontal part (43) of a 
hook. The pointed, conical head (2?) of the nail-shaped piece 
corresponds in position with the pomt of contact of the bases of 
two successive hooks, and at the broadest part protrudes side- 
ways between the latter. The tip of the nail-head projects be- 
tween the point (74) of the succeeding nail and the base (A?) of a 
hook, the two latter constituting a sort of socket in which the 
former appears to slide. This would seem to show conclusively 
that this complicated ring may be enlarged or diminished at the 
will of the animal. 
The faint radiating ridges (7) which occupy the central two- 
thirds of the adherent apparatus are attached one by one to the 
point (74) of the nail-shaped body just mentioned, and at right 
angles to it. The basal third of these radi is easily seen with 
a one-fourth-inch objective ; but even a one-eighth does not dis- 
tinctly trace the pointed end to the centre of this apparatus. 
Each radius (i) and the nail-shaped body (2!, 2?) seem to form a 
solid piece, a sort of Greek I’ whose angle is occupied by a 
faint membrane, or web (73), which extends from one-third to 
one-half the way along the nail, and nearly, or altogether, to the 
end of the tapering radius. This faint membrane appears to 
fill the whole space between the radii, in healthy animals. 
In dying specimens the adherent organ readily separates 
from the body, en masse; but shortly afterwards the striated 
membrane loosens from the circle of hooks ; and in a brief space 
of time the latter becomes disjomted, and each hook detaches 
from its fellow, but remains for a longer period in conjunction 
with its corresponding radius and nail-shaped piece *. 
* Various opinions (and all of them at variance with the one promul- 
gated in this paper) have been expressed in regard to the nature of the ad- 
herent apparatus and its motory appendages, the vibratile row of cilia. 
Siebold (Zeitschr. fiir wissenschaftl. Zool. Bd. i. p. 367), as the following 
translation shows, has mistaken the row of vibratile cilia ( g) for an undu- 
lating membrane and has entirely overlooked the velum (f). He says, 
‘** Among the Infusoria, the genus Trichodina is endowed with a distinct, 
undulating membrane, which, applied to the lower margin of the body, in 
the form of a circle, adheres to, and is supported by, a solid toothed ap- 
paratus not unlike a watch-wheel. In Trichodina pediculus this vibrating 
border is entire-margined ; in T. mitra... . the free border of this appears 
to be deeply and delicately frmged. Trembley, Goeze, O. I’. Miiller, Carus, 
Dujardin, and others have, in consequence of an optical illusion, considered 
this undulating membrane in T. pediculus to be a vibrating-cilia-crown.” 
