THE ANIMAL KINGDOM 



381 



the substratum. Membranelles are vibratile membranes 

 found in the region of the cystostome. 

 SUBCLASS 1. PROCTOCILIATA. Parasitic in the large 

 intestine of a number of amphibians. No cytostome; a single 

 type of nucleus; reproduce by binary fission. 



Example: Opalina ranarum, intestinal parasites of frogs and 

 toads. 



Fig. 214. — Diagram of the nuclear changes in Paramecium aurelia during 

 conjugation. A, union of conjugants; B, degeneration of macronuclei and first 

 division of micronuclei; C, second division of micronuclei; D, degeneration of 

 seven of the eight micronuclei in each conjugant; E, each conjugant with a single 

 micronucleus, which in F has divided into a stationary and micronucleus; G, 

 each conjugant with a synkaryon formed by the fusion of the migratory nucleus 

 of one with the stationary nucleus of the other conjugant; H, first reconstruction 

 division of the synkaryon to form two micronuclei (takes place in each of the 

 conjugants which now separate) ; I, second reconstruction division of the micro- 

 nuclei; J, two micronuclei transformed into two macronuclei; K, division of two 

 micronuclei and division of cell; L, two complete new individuals. {After 

 Woodruff, Foundations of Biology, copyright, The Macmillan Company. By 

 permission.) 



SUBCLASS 2. EUCILIATA. Macronucleus and one or 



MORE MICRONUCLEI PRESENT AND USUALLY A CYTOSTOME. 



Order 1. Holotrichida. Cilia rather uniform in size and dis- 

 tribution, and usually arranged spirally in parallel lines. The 

 longest cilia are about the mouth. Trichocysts are common. 



Example: Paramecium aurelia, found in fresh water has a 

 cytostome, gullet, and cytopyge; contractile and food vacuoles; 

 a large macronucleus and two small micronuclei. If samples 



