420 Prof. H. James-Clark on the Anatomy and 
follows the spiral course of the vibratory crown, and vanishes 
near the aperture of the vestibule. The vibratory crown con- 
sists of a single row of vibrating cilia, which winds along the 
margin of the spiral dexiotropic peristome, just at the edge of 
the cupuliform disk, and descends thence to the left of the 
vestibular aperture, and, entering it, plunges to the bottom of 
the vestibule in an unbroken line. Neither Trichodina nor 
any of the Vorticellidze possesses a vestibular lash or bristle ; and 
the latter is an optical illusion. The posterior truncate end of 
the body is margined by a well-defined annular velum, imme- 
diately behind which, and arising from the same basis, is a com- 
plete circle of vibrating cilia. The so-called adherent organ, or 
apparatus of hooks and radii, consists, first, of a distinct, sepa- 
rable, annular border, whose opposite faces are dissimilarly 
striated by perfectly straight, transverse ridges ; secondly, of a 
complicated circle of disseverable hooks, which are applied to 
the posterior face of the striated annular border, along its 
proximal edge; and thirdly, of a series of I'-shaped radu, which 
le one by one opposite the several hooks, and converge toward 
the axis of the basal plane of the body. The vestibule and ceso- 
phagus are as well marked, each in its own way, as in any of the 
Vorticellidee. The vestibule opens near, and posterior to, the 
cilia-crowned margin of the sunken cupuliform disk. The anus 
opens into the vestibule a short distance from its mouth, and 
on the right side. The contractile vesicle is a simple cavity, 
which performs its systole once in fifteen seconds. The repro- 
ductive organ is a knotted band whose antero-posterior thick- 
ness is much greater than at right angles to that ; and it lies, in 
the form of a crescent, near the base and transverse to the lon- 
gitudinal axis of the body. 
The extraordinary and almost incomprehensible position and 
form of the disk of this singular appendage of the Vorticellidan 
group seem to render it desirable that no pains should be spared 
to make the relations of its organs to each other as clear to the 
understanding as it is possible to do with the help of figures. 
The accompanying diagrammatic illustration of a longitudinal, 
sectional, or rather profile, view of Trichodina pediculus is parti- 
cularly intended to exhibit the outline of the sunken cup-shaped 
disk (c, c!) and its close connexion with the peristome (d!, a?) ; 
but, in addition to this, it is designed to show, in an outline 
sketch, the relations of the internal organs to the walls of the 
body. The contractile vesicle (cv), not being strictly in the 
plane of the section, is represented in dotted outline. The nu- 
cleus (m) is cut across its middle. The sigmoid figure of the 
