CILIARY CURRENT IN PARAMECIA 285 



revolution of the spiral. The action of the cilia against a solid 

 seems to be less effective than the free beat in the culture fluid 

 and so the animals are retarded at each contact. If this takes 

 place just before the animal enters the edge of a cloud of ink 

 the continued beating of the strong cilia of the oral groove, no 

 longer compensated for by the for\Yard or lateral movement of 

 the body, draws a funnel shaped mass of water from in front, 

 which may reach or exceed the length of the body. The pause 

 in the animal's forward progress is only momentary and is quite 

 easily overlooked, but it can be distinctly seen. Even in deeper 

 preparations, in watch-glasses, where the organisms may swim 

 freely without contact with the bottom of the dish the condi- 

 tions of observation are frequently such as to give the impres- 

 sion that the cone is produced much more frequently than is in 

 reality the case. \Mien a dilute suspension of India ink is used 

 to form a sharp edged cloud in the culture dish, the ink rapidly 

 settles and spreads out along the bottom of the dish so that the 

 edge of the cloud can be seen onlj^ with a deep focus of the 

 microscope. Hence only those animals which are swimming 

 near the bottom are visible and their frequent contact with the 

 bottom subjects them to almost constant mechanical retarda- 

 tion (fig. 2). But retardation owing to contact with the substra- 

 tum is not the only cause of the formation of feeding-cones in 

 moving paramecia. 



The water currents produced by the cilia of Paramecium have 

 by various investigators been most thoroughly studied in ani- 

 mals whose movements were mechanically retarded so that the 

 movements of the cilia might be observed. This is generalh^ 

 brought about by the addition of gelatin or some other colloid 

 to the water. The writers made extensive observations under 

 such conditions with the following results and conclusions: 



Animals in quince-seed jelly so thick that they force their way 

 through it with difficulty, always produce apparently continu- 

 ously, a very marked feeding cone, whether they are swimming 

 forward or backward; and in dividing animals which lack the 

 oral groove the cone is quite as large as is that produced by nor- 

 mal animals. Such jellies are, however, never homogeneous and 



