376 MUS. L. J. YELET — CONTRIBUTION TO THE 



cast out from the living animal ; but Prof. Bourne and others had 

 considered this motion to be possibly molecular, and in my 

 previous observations it had not been possible to satisfy myself 

 absolutely that the motion was not due to currents created in the 

 water by the activity of the pseudopodia, or to other physical 

 causes. The seven Pelomyxce used in this investigation were 

 healthy but sluggish specimens, in which rods and refringent 

 bodies were very abundant and the former unusually large and 

 thick. The method of observation adopted was to crush a 

 Pelomyxa in a drop of water, so as to set free the bacteria, and to 

 watch these continuously for periods of several hours without 

 intermission (generally for 3 hours in the morning and 2 hours 

 in the afternoon), without removing the eye from the microscope. 



Motility. — The rods, when set free, moved at first actively at 

 the free edge of the animal, gradually becoming more sluggish 

 and eventually coming to rest altogether. As a result of con- 

 tinuous observation directed to this one point only, I was able to 

 establish on the first day that the motion was undoubtedly one 

 of translation. The rods moved even very rapidly at times, in 

 opposite directions and in every direction ; the Pelomyxa having 

 been killed by crushing, there were now no currents due to motion 

 on the part of the animal ; further, the drop was not allowed to 

 evaporate, hence there could be no currents due to evaporation. 



The motion of the rods was both horizontal and vertical, and 

 could often be seen to change from one plane to the otlier ; 

 several times a rod was observed to swim vertically and then 

 turn over and travel away horizontally. The motion was of the 

 kind always associated with the presence of flagella, and suggested 

 the presence of flagella at each pole, or possibly all round. 

 While watching a large rod of six joints in one of the "pools" 

 made in the interior of the Pelomyxa by crushing, it was seen 

 to swim actively in the pool and then to pass through an 

 intervening bridge of protoplasm into a second pool. By 

 focussing the rod carefully during transit it was possible to be 

 certain that it passed through, not under or over tlie protoplasm, 

 and this with a peculiar boring action like that of a bradawl when 

 used to make a hole, viz., a revolution through half of a circle and 

 back. 



The attention of other observers was called to the motion of 

 the rods, and all testified that it was transitional. 



