246 WILLIAM HATCHETT JACKSON. 
hooked ring (r., figs. 1, 2, 6) which so clearly approximates 
this Infusorian to Trichodina. Externally is a row of 27 
hooks (h., figs. 1, 7) all curved in one direction and im- 
planted by a broad base on the ring (r., fig. 7) from the 
inner side of which arise slender processes—the radii 
(r', fig. 7), gradually tapering to their extremities, somewhat 
of a sinuous figure, and equal in number to the hooks. These 
radii are imbedded in the substance of the animal. They 
pass inwards below the surface of the central depression into 
the body, as may be seen from a careful examination of figs. 
2and 6. All this apparatus is quite rigid, of a greenish 
colour, and composed of some peculiar substance, the ring 
seen under a high power being streaked in a direction 
parallel to its circumference, while both hooks and radii are 
perfectly clear. James Clark! gives te the hooks and radii 
of T. pediculus a very complex structure, but nothing similar 
could be detected in this animal. On the other hand, the 
ring is here more complex than the similar apparatus of 
T. (Urceolaria®) mitra and Trichodinopsis*), which are desti- 
tute of teeth but have an apparently twisted structure. 
Of the central depression nothing much is to be said. It 
is cup-shaped (d., fig. 2) and is unchangeable in form. Its 
limiting wall is perfectly hyaline, as mentioned before. 
On the oral side of the disc, i. e. behind the circle of 
motor cilia when the disc is turned towards the observer as in 
fig. 1, is the row of sete (s., figs. 1, 2), if such a name is 
justifiable. In the front view (s., fig. 1) they can be seen 
projecting slightly beyond the ends of the motorial cilia. In 
number they are sixteen. ‘They are long, thickish at the 
base (cf. fig. 2), then rapidly thinning out and becoming finer 
at their extremities than are the cilia. In substance they are 
slightly rigid, not so much so as to be absolutely immovable 
or incapable of moving to a certain extent. Once the 
animal moved them in such a manner that they were 
arranged in the front view radially and in a plane parallel 
to the surface of the disc, that is, nearly at right angles to 
the position in which they are drawn in fig. 2. They are 
exceedingly difficult to see—in fact invisible—until the mirror 
of the microscope is adjusted at the proper angle to the 
object. What their functions may be, is doubtful. The only 
other example of anything at all similar is furnished by the 
circlet of setae or setee-like cilia in Halteria, attached in this 
1 Loe. cit., pp. 4, 14, 15, Pl. IX, fig. 18. 
? Stein, ‘ Organisation der Infusionsthiere,’ Abth. II, 1867, p. 147. 
3 Claparéde and Lachmann, Etudes, vol. i, Pl. IV, figs. 1, 2. Stein, 
loc. cit., Abth. II, p. 146. 
