32 AET. 11. A. IZUKA : OBSERVATIONS ON THE 



as to almost expose the mud at the bottom and the latter by 

 slowly adding fresh water to a depth of about two feet. In the 

 river, the bottom-temperature was found to rise 1-2°C. higher 

 during the flood than at the ebb, the surface maintaining the 

 same temperature all the time. This periodical change in bottom- 

 temperature could not very well be introduced into the aquarium, 

 but this seemed to excercise no influence upon the swarming 

 process. I regret that I omitted to ascertain by experiment 

 whether or not the worms, when left in standing water that 

 showed nothing like the ebb or the flood, would have swarmed 

 out at the right time. 



The epitocœ that have swarmed out in the aquarium continue 

 to swim about for a longer or shorter period, sometimes for several 

 hours, though the swimming may at times be interrupted by 

 pauses in which they sink to the bottom and remain motionless. 

 In many cases the distended body-wall becomes rent during the 

 exertions of swimming ; this soon puts an end to the swarming 

 career. In other cases, they may remain for a considerable while 

 uninjured save at the posterior torn end. Such individuals become 

 gradually less energetic in their movements, finally to rise no 

 more from the bottom, but soon to become ruptured in the body- 

 wall. It may fairly be said that in twenty-four hours at the 

 longest the energy of the worms becomes completely exhausted 

 in all cases, unless, as before mentioned, their movements be 

 restricted by denying them enough water to swim in, so that it 

 seems exceedingly probable that the worms which have once 

 swarmed out in the river never join in the swarm of the day 

 following. I see no ground, to doubt that the fate which I have 

 observed to be fall the swarming epitocœ in captivity, is in general 

 the same as that which happens to those under natural conditions. 



