CILIOPHORA, CI LI ATA, PROTOCILIATA 335 



an individual varies: thus, one in Paramecium caiidatum; two 

 in P. aurelia; three in Spirochona; four in Paramecium multimi- 

 cronucleatiim; up to as many as 28 in Stentor roeseli. At the time 

 of reproduction it increases in size and divides mitotically. Dur- 

 ing conjugation it apparently undergoes a meiotic division. 



The Protociliata possess from one to many hundreds of 

 nuclei of a uniform structure and numerous ovoid or spindle- 

 shaped bodies, the nature of which is open to speculation. Some 

 authors think that they are nuclei — micronuclei (after Hickson) 

 or macronuclei (after Konsuloff). Metcalf considers that each 

 nucleus possesses both metabolic chromatin and reproductive 

 chromatin, the former being seen as large flattened peripheral 

 masses and the latter, as smaller spheroidal granules. 



In all except a comparatively small number of astomous 

 forms, there is a cytostome located either at the anterior end or 

 between this point and the middle of the body. In its simplest 

 form the cytostome is represented by a small opening on the 

 pellicle, which may or may not be closed when the animal is not 

 feeding. The cytostome opens into the cytopharynx (or gullet), 

 a canal which ends in the deeper portion of the endoplasm. In 

 the cytopharynx there may be present an undulating membrane 

 to facilitate the intaking of the food. Occasionally the cytostome 

 is surrounded by trichites (p. 34). When the cytostome is not 

 at the anterior region as for instance in Paramecium, there is a 

 peristome (or oral groove) which starts at the anterior end and 

 runs posteriorly. The ridges of the peristome are ciliated so that 

 food particles are thrown down along it and ultimately into the 

 cytostome which is located at its posterior end. Solid waste 

 particles are extruded from the cytopyge, or cell-anus, which is 

 usually noticeable only at the time of actual defecation (p. 34). 



Following Metcalf, the Ciliata are here divided into two 

 subclasses : 



Two to many nuclei of one type; sexual reproduction copulation 



Subclass 1 Protociliata 



Nuclei of two types: macronucleus and micronucleus; sexual reproduc- 

 tion conjugation Subclass 2 Euciliata 



SUBCLASS 1 PROTOCILIATA METCALF 



The members of this group are parasitic in the intestine of 

 Amphibia with the exception of a few species which occur in 



