158 



PHYLUM: PROTOZOA 



Fig. 70. — Diagrammatic Figure of Parame- 

 cium caudatum ( x ca. 500). (From Minciiin, 

 1912, AFTER Lang.) 



P., Peristome groove; o, mouth; ces., oesophagus with 

 undulating membrane; f.v.', food vacuole forming 

 at end of oesophagus; /.r., other food vacuoles; c.v., 

 contractile vacuole with surrounding channels lead- 

 ing to it; ex., excretory crystals; N, macronucleus; 

 74, micronucleus ; tm, trichocj'sts ; al., alveolar layer; 

 p., pellicle; um, undulating membrare 



threads are discharged. A de- 

 finite mouth opening or cyto- 

 stome may, or may not, be 

 present. 



Though the Ciliophora agree 

 with one another in the posses- 

 sion of cilia, they differ funda- 

 mentally as regards their nuclei. 

 In what may be regarded as the 

 more primitive forms (Opali- 

 nata) there are present in each 

 individual two or more nuclei 

 which are all of one type, in 

 which respect an approach to 

 the Plasmodroma is made. 

 When syngamy occurs uninu- 

 cleated forms are produced, and 

 these, which are gametes, unite 

 in pairs, with complete fusion of 

 the bodies and nuclei. In other 

 forms there are typically two 

 morphologically distinct nuclei, 

 one of which is a macronucleus 

 and the other a micronucleus. 

 During syngamy the macro- 

 nucleus disintegrates and takes 

 no part in the process, while 

 the micronucleus divides. Two 

 individuals associate, and one 

 of the daughter micronuclei of 

 each individual migrates into 

 the other and unites with its 

 remaining daughter micronu- 

 cleus. When this has taken 

 place, the associated or con- 

 jugating individuals separate 

 and continue to lead an inde- 

 pendent existence. On the basis 

 of this distinction Metcalf (1918) 

 recognizes two groups, the 

 PROTOCILIATA and the 

 EUCILIATA. The members 



