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INFUSORIA AS PARASITES. 
By W. SAVILLE KENT, F.L.S., E.R.M.S., &c. 
[Plates YII. and YIII.} 
A N irresistible balo of fascination is ever associated with the 
structural details and life-phenomena of those beings to 
whom other and mostly higher representatives of the animal 
kingdom extend shelter and protection, and afford, if not direct 
sustenance, free lodging and a modus vivendi. 
To the practical biologist such animal types are of peculiar 
interest, since such an acquired and artificial phase of existence 
is most often correlated with structural modifications of the 
most abnormal order, and which in themselves testify volumes 
as to the capacity and tendency of organic forms to adapt them- 
selves to surrounding conditions, and, losing all trace of their 
pre-existing distinctive features, to develope into something 
different, or into what, for convenience sake in zoologic ter- 
minology, is denominated a new or independent ‘ species/ Such 
forms, again, recommend themselves to the evolutionist as the 
latest products of Nature’s crucible ; since, many of them 
being the satellites of the highest and most recently developed 
organic types, they must, pari passu, have acquired their own 
typical characteristics still more recently. 
So far, the examples of parasitic existence with which the 
student of zoology is most intimately conversant, are found 
within the precincts of the Arthropodous and Vermiform sub- 
divisions of the invertebrate sub-kingdom. Among the groups 
or types, which may be suitably cited in this connection, may be 
mentioned more especially the innumerable Entozoic and Ecto- 
zoic Worms, comprehended within the several orders of the 
Trematoda, Cestoidea, Nematoda and Acanthocephala ; also the 
retrograde and singular Crustacean forms, represented by the 
ectoparasitic Lernaeidse and other Epizoa, and including also, as 
near relatives of the Barnacles and Acorn- shells, or Cirripedia, 
NEW SERIES, VOL. IV. NO. XVI. X 
