The ciliates of domestic animals all 

 belong to the class Ciliasida. The nuclei 

 of this group are unique in the animal king- 

 dom. Every individual (except in a few 

 amicronucleate strains) has a micronucleus 

 which contains a normal set of chromo- 

 somes, and a macronucleus which contains 

 an indeterminately large number of sets 

 and is actually /;-ploid rather than poly- 

 ploid. The micronucleus is active in re- 

 production, while the macronucleus has to 

 do with the vegetative functions of the or- 

 ganism. 



The ciliates have either simple cilia 

 or compound ciliary cirri or membran- 

 elles in at least one stage of their life 

 cycle. They also have an infraciliature in 

 the cortex beneath the pellicle, composed 

 of the ciliary basal granules (kinetosomes) 

 and associated fibrils (kinetodesmata). 

 The infraciliature can be stained with sil- 

 ver, forming the so-called silver-line 

 system. Reproduction is by transverse 

 binary fission, in contrast to the longitu- 

 dinal fission seen in the flagellates. True 

 sexual reproduction, in which gametes fuse 

 to form a zygote, is absent, but conjuga- 

 tion, in which there is an exchange of mi- 

 cronuclear material between two individ- 

 uals, may be present. 



Chapter 13 



THE CILIATES 



The great majority of ciliates are 

 free-living, but a number are parasitic. 

 Their classification has recently undergone 

 considerable overhauling, and they are 

 now arranged in 26 orders and suborders 

 belonging to 2 subclasses (Corliss, 1956, 

 1957, 1959). This classification is based 

 on recent work by the French school, and 

 particularly by Faure-Fremiet, on the 

 silver-line system, and is more natural 

 than the earlier one. Terms used in des- 

 cribing the ciliates are defined by Corliss 

 (1959). Corliss (1961) has reviewed the 

 whole group. 



The characteristics of the taxa found 

 in domestic animals have been given on 

 pp. 34-38. In the subclass Holotrichasina, 

 the body ciliature is typically uniform and 

 simple. Buccal ciliature (an adoral zone 



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