30 



INFUSOKIA. 



adult, but are not found when they are encysted. In the 

 second, cilia are only present during the larval stage, their 

 place being taken by suckers and tentacles. None of the latter 

 are parasites on metazoa. The Ciliata are the most complex of 

 the Protozoa, and several occur as parasites in metazoa. In 

 form they are typically ovoid, one pole being directed forwards 

 in swimming, whilst in creeping species the body is flattened ; 

 others, as the Bell Animalcule ( Vorticella), are fixed by a stalk. 

 They are of definite form, the body being enclosed by a cuticle. 

 In this cuticle is an opening, the cystotome or mouth, and there 



may be a definite anus or cytopyge. 

 The mouth is merely a pore passing 

 through the ectoplasm. 



Ciliata reproduce by fission or 

 budding (gemmation), and also when 

 encysted by sporulation. 



Parasitic forms encyst when out 

 of their host, and then can remain 

 dormant until taken up by another 

 host. 



Those that are parasitic occur 

 in the digestive tract and other 

 internal cavities, but never as tissue 

 parasites. There are four orders — 

 (1) Holotriclia, in which the cilia 

 are of even length and spread all 

 over the body ; (2) the Hetem- 

 triclia, in which a special adoral 

 zone of larger cilia is always present ; (3) HypoMcha, which 

 are creeping forms and flattened (not parasitic) ; and (4) Peri- 

 tricha, which are fixed forms like Vorticella, without locomotar 

 cilia. 



Balantidum roJi (fig. 7) is one of the Heterotricha. It is 

 found in the rectum, &o., of pigs and man. These white 

 ciliata are found as free-swimming bodies in the rectal matter. 



Fig. 7. — CiMATE Protozoan 

 (Balantidum coU). 



a, pseudo-anus ; n, 

 contracttle vacuoles ; 

 (Stein). From Par. 

 Nftumann.) 



nucleus ; vc, 

 p, peristome 



