the Ciliate Infusoria. By G. J. Allman. 171 
vast assemblage of images confused and ill-defined by tlieir very 
multiplicity and by the condensation -which would be inseparable 
from their treatment. 
While thus imposing on myself these necessary limits, it is 
almost at random that I have chosen for this year’s address some 
account of the progress which has recently been made in our know- 
ledge of the Ciliate Infusoria — a group of organisms whose very 
low position in the animal kingdom in no way lessens them interest 
for the philosophic biologist, or their significance in relation to 
general morphological laws. 
To enable you to form a correct estimate of the value of recent 
researches, it may be well to bring before you in the first place, as 
shortly as possible, the chief steps which have led up to the present 
standpoint of our knowledge of these organisms. 
It is scarcely necessary to remind you that the first important 
advance which during the present century was made in our know- 
ledge of the Infusoria dates from the publication of the great work 
of Ehrenberg,* whose unrivalled industry opened up a new field of 
research when, by his expressive figures and well-constructed 
diagnoses, he made us acquainted with the external forms of whole 
hosts of microscopic organisms of which we had been hitherto 
entirely ignorant, or which were known only by such figures and 
descriptions as the earlier observers with their very imperfect micro- 
scopes were able to give us. 
Ehrenberg, however, as we all know, did not content himself 
with portraying the external forms of the microscopic organisms 
to whose study he had devoted himself, but sought also to deter- 
mine their internal structure, of which scarcely anything had been 
hitherto known. In this direction, no less than in the other, the 
perseverance of the celebrated microscopist never flagged ; but, 
unfortunately, at the very commencement of his researches he 
slid into a misleading path, and was never again able to find the 
right one. 
Everyone knows how Ehrenberg, in accordance with precon- 
ceived notions of the high organization of all animals, attributed to 
the Infusoria a complicated structure ; how, while he rightly dis- 
tinguished them from the Botiferm with which they had been 
confounded by 'previous observers, he yet regarded them as inti- 
mately related to these representatives of a totally different type ; 
and how, in attributing to them a complete alimentary canal with 
numerous gastric offsets, he took this feature as their most impor- 
tant character, and designated them by the name of Polygastrica. 
And it is probably a matter of surprise to many of us, that with the 
overwhelming mass of evidence which subsequent research has 
brought to bear against the truth of the polygastric theory, the 
* ‘ Die Infusionsthierchen als vollkommene Orgamsmen.’ Leipzig, 1838. 
