286 S. O. MAST AND K. S. LASHLEY 



the cone seems to result from the fact that the organisms force 

 their way with difficulty between the masses of denser jelly while 

 the more fluid parts of the preparation, with the granules which 

 they contain, are easily set in motion and sucked towards them. 

 After the animals have been in the jelly for a short time it is cut 

 up into canals, each marking a place through which an animal 

 has previously passed. These are indistinctly visible and may 

 be traced for some distance through the preparation. The ani- 

 mals tend to follow these open paths where they meet with less 

 resistance and in swimming through the less dense medium they 

 produce practically no cone. In giving the avoiding reaction 

 under these conditions they draw in a cone of water from behind 

 momentarily but if the backward swimming follows the path 

 along which they have just advanced the cone disappears as 

 soon as the rate of locomotion becomes uniform ; only when they 

 force their way through the denser jelly do they produce the cone. 



Dense suspensions of starch grains, carmine and India ink act 

 in the same way as the quince-seed jelly. The ordinary culture 

 fluid from which the animals are usually taken for study often 

 contains transparent masses of bacteria which are visible only 

 with dark ground illumination. These probably also have the 

 same effect as the jelly in retarding the animals and producing 

 the cone; and it is highly probable that the cones observed and 

 recorded in many instances were caused by these invisible but 

 resistant substances, locally distributed throughout the solu- 

 tion, and that the cones were produced only when the animals 

 entered the regions containing them. Thus it is evident that 

 mechanical retardation is one of the principal causes of the for- 

 mation of feeding-cones in moving paramecia. They are, how- 

 ever, also produced without any such retardation as will be 

 shown presently. 



In some cases when the reactions of the paramecia at the edge 

 of a cloud of ink were being observed, the animals were seen to 

 draw out a cone of ink under conditions where they were cer- 

 tainly not mechanically retarded. This happened most fre- 

 quently when the animals either paused before entering the 

 cloud or turned aside without entering. In the latter case, which 



