IV. CILIATA: HOLOTRICHA 



195 



also the macronucleus which controls the body processes, and hence is 

 the somatic nucleus. In other words, fertilization in the Ciliates leads to 

 a complete new formation of the nucleus and thus to a new organization 

 of the organism. 



In most Ciliata the conjugating individuals are similar, the fertiliza- 

 tion is mutual, and the individuals separate later. In the Peritricha 

 (mostly sessile forms, fig. 152), on the contrary, the resemblance to 

 fertilization in the Metazoa is strengthened in that there is a sexual differ- 



^ entiation and a permanent fusion of the con- 



"^ " , jugating individuals. Some animals — the 



y ^, macrogametes — retain their size and sessile 



' habits; others by rapid division produce 



( groups of markedly smaller microgametes. 



J The latter separate and fuse completely 



with the macrogametes. The nuclear 



phenomena are much the same as with 



Paramecium, allowance being made for the 



permanence of the fusion. 



Fig. 153. i-iG. 154. 



Fig. 153. — Stentor polymorphiis fafter Stein), a, peristomial area; ft, roof of 

 hypostome; g, contractile vacuole; n, nucleus; 0, cytostome; ;•, adoral ciliated spiral; t, 

 hypostome (excavation for mouth). 



Fig. 154. — Balantiaium coli (after Leuckart). 



Order I. Holotricha. 



The Holotricha are the most primitive Ciliates, since the cilia on all parts 

 of the body are similar; being at most slightly stronger at one end of the body or 

 inside of the cytostome. Best known are the species of ParamiFciuin* (fig. 150) 

 occurring in stagnant water. Opalina ranarum* lives in the intestine of the frog. 

 It lacks mouth, has numerous similar nuclei, no micronucleus and no conjuga- 

 tion. The small encysted Opalintv pass out with the faeces, and are eaten by the 

 tadpoles, which thus become infected. 



