376 BIOIJHiY OF THE PROTOZOA 



the fertilization phenomena do not follow the usual routine of other 

 ciliates, microgametes being formed and fusion being permanent. 



Conjugation always results in physical reorganization of the proto- 

 plasm the old macronueleus is broken uj) and the fragments are 

 absorbed in the cytoplasm while a new macronueleus and new micro- 

 nuclei are difterentiated from products of the first or second division 

 of the amphinucleus after fertilization (see Chapter XI). A similar 

 reorganization takes place at regular intervals of thirty days (P. 

 aurcUa) or sixty days (P. cauddtinn) according to Woodruff and 

 P>dmann (1914) who termed the phenomena accompanying this 

 method of reorganization "endomixis (p. 540). In other types of 

 ciliates similar asexual processes of reorganization take place under 

 the protection of a cyst (for significance of reorganization see 

 Chapter XII). 



The classification adopted here has been generally accepted, and 

 with few changes, since the great work of Biitschli in 1888. We 

 divide the sub-phylum into two classes of unequal size, viz., Ciliata 

 and Suctoria. 



Class I. CILIATA, Butschli. 



The common features of the Ciliata have l)een outlined in the 

 discussion above. The distribution and ditferentiations of the 

 motile organs form the basis for division of the Class into five 

 Orders: Holotrichida; Ileterotrichida; Oligotrichida; Hypotrichida 

 and Peritrichida. Motile organs are alike and but slightly differ- 

 entiated in the Holotrichida where adoral zones are absent. A 

 general covering of cilia, and with an adoral zone of membranelles 

 in addition is the main characteristic of the Heterotrichida ; in 

 Oligotrichida body cilia are absent or greatly reduced but an adoral 

 zone is present which as in Ileterotrichida and in Hypotrichida 

 turns to the left from the mouth. In Hy])otrichida the motile 

 organs are on the ventral surface and are highly differentiated. In 

 Peritrichida an adoral zone which here turns to the right from the 

 mouth alone is present in the ordinary vegetative condition. Fur- 

 ther diagnotic features will appear in connection with the different 

 orders. 



Order I. HOLOTRICHIDA, Stein. 



Ciliates with generally uniform body cilia and without a special- 

 ized zone of membranelles. Mouth normally present (absent only 

 in Astomina) and with (Trichostomina) or without (G^'mnostomina) 

 oral membranes. The mouth may be terminal, subterminal or at 

 any point on the ventral surface or right side. Proboscis-bearing 

 forms are common; spines, bristles and caudal filaments not uncom- 

 mon; and pharyngeal baskets are highl\' developed in one family 

 (Chlamydodontidse). N^utrition is holozoic or parasitic (Astomina) ; 

 reproduction, normally, is by transverse division. Encystment is 



