404 Prof. H. James-Clark on the Anatomy and 
relations of the type and of the two extremes are never lost sight 
of amid the growing complexity of the organization. 
Among the many forms which more than usually excite the 
interest of the observer, there is no one in the whole class of 
Protozoa that surpasses the allurements of the remarkable crea- 
ture which forms the subject of the present memoir. This is 
accounted for by a twofold reason,—in the first place, because it 
possesses such an unlooked-for degree of complication in its 
organization ; and secondly, because it seems to stand inter- 
mediate between the two great groups of Ciliata—the dewio- 
tropic on the one hand, and the /zotropic on the other. The 
transitional forms in all departments of the animal kingdom are 
eminently suggestive, but none more so than the genus Tricho- 
dina. Combining i in one animal the typical forms of two groups, 
and yet so singularly individualistic as to be confounded neither 
with the one nor with the other, the elaborate solution of the 
relations of the various members of its organization to each 
other, and the tracing of their homologies with those of the 
groups on either side, engage the attention no less deeply, and 
none the less worthily, than if it were occupied in the investiga- 
tion of the most profound philosophical problem. 
An attempt, therefore, at a full life-history of this animal be- 
comes an effort at something more than a mere specific description 
without an aim; and whatever apparent triviality of detail there 
may seem to be in it, the consciousness that no one part of an 
organization is without relation to some other part leads the 
author to the opinion that an investigator should never under- 
take to assume what is of importance and what is not. Itis no 
unfrequent occurrence that what at one time has been deemed 
worthy of very slight consideration, becomes at another the 
paramount object in a course of scientific research. Nature 
is not to be represented in full detail by the broad touches and 
counterfeiting portraiture of a Vandyck, howsoever striking and 
suggestive the likeness may be ; in order to beara closer inspec- 
tion, her image must needs be mapped and copied by the more 
matter-of-fact hand of the humbler Flemish artist. 
§ 1. Hasirat.—tThis species (Pl. VIII., Trichodina pediculus, 
Ehr.) is found in great abundance creeping over the body, and 
even to the tips of the tentacles, of our common brown and 
green freshwater Hydras (H. fusca and H. viridis, Trembley). 
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. 
Notwithstanding the apparent rigidity of the chitinous unci- 
nate ring of the base, the latter possesses the greatest degree of 
