169 QUARTERLY CHRONICLE. 
Natural History, and contains a very minute account of the 
infusorian which forms its subject. Trichodina pediculus is 
found in great abundance, creeping over the body, and even 
to the tips of the tentacles, of our common brown and green 
fresh-water Hydras. Oftentimes it may be seen with the 
middle of its base applied directly over the centre of a group 
of nettling organs, the former fitting the latter like a cap, 
and without seeming to disturb the Hydra in the least. It 
appears that this animal has been much abused in European 
works on Infusoria, its portrait having been taken from speci- 
mens when under pressure, thus causing its true doubly 
conical, dice-box form to assume the appearance of a broad 
cylinder or a turban. In describing the cesophageal cilia of 
this animal, Professor Clark says that the so-called “ bristle 
of the vestibule” of Vorticellide, which was first described 
as such by Lachman, is an optical illusion. He has satisfied 
himself that it is an effect produced by the right and left 
rows of cilia, and has confirmed his opinion by observations 
on Epistylis, Carchesium, Vorticella, and others. One great 
test of the genuine character of the filament would have been 
its disappearance when the focus was slightly altered; but 
Professor Clark found that it did not disappear, as would be 
the case in observing the outline of a transparent cylinder. 
After dealing very carefully with the prehensile cilia, the 
author passes on to those devoted to locomotion and the 
other prolongations of the body adapted to that function. 
The adherent organ is one of these, and is a complex appa- 
ratus, which altogether forms a thin circular disc, whose 
border reaches to the margin of the base, or, in other words, 
to the inner edge or line of attachment of the velum. About 
one third of the radius of the adherent organ, at the peripheral 
margin, is occupied by a striated annular membrane, which 
is separable from the rest of the apparatus. It lies in front 
of the centrifugally projecting hooks with which the organ 
is provided, but is closely pressed against them, and extends 
centripetally as far as their bases. This membrane is pos- 
sessed of two sets of striz, which radiate from its inner to its 
outer margin. One set of striz occupy the anterior face, 
and are comparatively quite coarse, and in number about 
ninety-six, 7. e. about four times the number of the hooks of 
this organ. They lie wide apart, and are arranged so uni- 
formly that two traverse the interval between every two 
hooks, and two overlap every hook, where they run to the 
proximal margin of the membrane. ‘The other, or posterior 
set of striz, is much more readily detected than the anterior 
one, and the striz are about three times as numerous. The 
