CILIATA. 45 



to four micronuclei ; of these three abort, and one divides again 

 to form the two pronuclei, as we may call them. One of these 

 migrates into the other gamete, and fuses with its stationary pro- 

 nucleus to form the zygote-nucleus. This undergoes two bipartitions, 

 during which the gametes separate and the old macronucleus dis- 

 appears. The exconjugates now possess four nuclei, all derived 

 from the zygote-nucleus. Of these, two become micronuclei and two 

 macronuclei of the first bipartition, which takes place at from four to 

 nine days after the separation. So that the exconjugate has for some 

 time double the ordinary nuclear apparatus, and the first bipartition 

 takes place quite independently of the nuclear division. For some 

 days after conjugation the exconjugates take no food, and appear 

 to be without a mouth and gullet. They acquire the latter and begin 

 to feed about twenty-four hours before the first bipartition. 



The mode of life of the Ciliata is very various. Most of them lead 

 an independent life ; some are carnivorous and others herbivorous. 

 The former are very rapacious, and may take up even RoHfera. 

 Some, as AmpMleptus, select fixed Infusorians, as Carchesium and 

 Epistylis, for their prey, and swallow them down as far as the origin 

 of their stalk. They then, while fixed on the stalk, secrete a capsule, 

 and divide into two or more individuals. Some, as the mouthless 

 Opalina and many Bursaridic, are parasitic in the intestines and 

 bladder of Vertebrata. To these belong the Balantidium coli, from 

 the large intestine of man. (Fig. 40.) 



Order 1. GYMNOSTOMATA. 



The mouth is usually closed except during inception of food, and 

 is without undulating membranes. The pharynx when distinctly 

 developed is without ciliary structures, but is usually provided with 

 a rod -apparatus or a modification of one. The food is always 

 swallowed, never taken in by a whirlpool. Ciliation usually 

 holotrichous, but often more or less reduced. 



Fam. 1. Enchelina. The mouth is terminal or sub-terminal, is usually 

 round, rarely slit-like. Anus usually terminal. Conjugation terminal. 



Sub-fam. 1. Holophryina. Without tentacular structures. Holophrya 

 Ehrb., m. and f.w.*; Urotricha Clap, and L. with caudal bristle, f.w. ; 

 EnchcJys Hill, m. and f.w.; Spathidium Duj., f.w. ; Cliccnia Quennerstedt, 

 m. ; Prorodon Ehrb.; Dinophryu Btitschli, f.w.; Lacrymaria Ehrb. 



Sub-fam. 2. Actinobolina. With retractile tentacular organs and cilia. 

 Actinobolus Stein, f.w. 



* in., f.w., and infus. are abbreviations for marine, fresh-water, and infusions. 



