434 



SPECIFIC MICRO-ORGANISMS 



eight nuclei, of which four enlarge to become macronuclei, one re- 

 mains as a micronucleus and three disintegrate and disappear. 

 The one micronucleus then divides by mitosis and the cell divides 

 to form two paramaccia, each containing one micronucleus and two 

 macronuclei. The next division gives rise to cells containing 

 A the normal number of nuclei, one micronucleus and 



one macron ucleus. 



The paramecia are large saprophytic organisms, 

 easily kept under cultivation in the laboratory, and 

 they have been very extensively studied. Many 

 conceptions founded upon these 

 studies are considered to have a 

 broad bearing upon the physiology of 

 all living cells. For example Jen- 

 nings 1 has found that conjugation 

 serves two purposes, (i) to provide 

 chemical stimulation of cell division 

 and (2) to insure variety in the de- 

 scendants. The variety in the de- 

 scendants is a result of the exchange 

 of nuclear material. Calkins 2 has 



FIG. 209. Paramaecia drawn at .. . .. ... 



the same magnification. A. Para- discovered a specialization of func- 



m&cium caudatum. 

 cium putrinum. 



B. ParamcE- 



tion in paramecium in respect to con- 

 jugation and concludes that in some 

 of the descendants of an ex-conjugant the ability to conju- 

 gate is in abeyance, thus suggesting a resemblance to the somatic 

 cells of a metazoon, while other descendants retain this function 

 and are therefore analogous to the germ cells of a metazoon. 



Three other species of paramecium are recognized, namely, 

 P. aurelia, P. bursaria and P. putrinum. 



Opalina Ranarum. This is a common parasite in the in- 

 testine (cloaca) of the frog. It reaches a large size, 600 to Sooju 

 in diameter, is flattened and somewhat irregular in outline. The 



1 Harvey Lectures, 1911-12, pp. 256276. 



2 Proc. Soc. Exp. Biol. and Med., 1913, Vol. X, pp. 65-67. 



