84 DAVENPORT ACADEMY OF SCIENCES. 



Kellicott, in western New York, reports a form without the pos- 

 terior tuft of cilia, which perhaps is the European variety, 

 ParamcEcium aurelia. 



This species, by reason of its widespread distribution and 

 abundance, is readily accessible to the student of biology and 

 should be examined by him because some interesting phenomena 

 are presented by it. 



The gross features of intracellular digestion may readily be 

 followed. As food particles enter the cytoplasm they are col- 

 lected into minute spherical masses by the whirling motion of the 

 current of water and each food-mass, enclosed by a film of water, 

 is caught up by the streaming cytoplasm and slowly transported 

 back and forth until the digestible portions have been so reduced 

 that they can be assimilated. The indigestible material is thrown 

 off at the anal opening, which is ventral in position, about half 

 way between the mouth and the posterior extremity. 



The position of the macronucleus, close to the inner end of the 

 pharynx, is of no little significance, for from this point intracell- 

 ular ferments can most readily be given off to the incoming food. 



The contractile vesicles are distinct and often may assume a stel- 

 late appearance, especially when mechanical pressure is applied. 



Temporary conjugation of individuals of the species may fre- 

 quently be observed if infusions remain for some time in the 

 laboratory. Under these conditions large numbers of individuals 

 may suddenly enter into a state of conjugation and after remaining 

 united for a few days the organisms quite as suddenly separate, 

 only to repeat the process after a period of more or less duration. 



Fig- 137- 



During the period of union of a pair some remarkable physio- 

 logical changes take place which have been carefully worked out 

 by Maupas and Hertwig. The micronucleus of each individual 

 divides and each portion again divides, three of these parts appar- 

 ently degenerate, the other again divides, one part of which 

 remains in a state of rest, the other passes to the companion 

 organism and fuses with the resting portion of the macronucleus 

 there. The macronucleus then breaks up, its fragments being 

 scattered throughout the cell, finally degenerating, the'new nuclear 

 elements being constructed from the fused micronuclear portions. 

 Fig. 138. 



