FORMATION OF NEW COLONIES OF MEGALOTROCH A. 187 



to get as near the source of light as possible. But if the ball is 

 placed in artificial darkness they very soon begin to form a per- 

 manent colony. 



The method of forming this permanent colony is interesting. 

 When no longer influenced by the light the ball begins to move 

 about the dish in an apparently aimless manner. If in this wan- 

 dering it chances to come against some piece of water plant or 

 other object many of the young rotifers turn their trochal discs 

 towards this, thus checking the progress of the ball. This reac- 

 tion is brought about by purely tactile stimuli. If a clean needle 

 is placed in front of a swimming ball, the latter will stop and the 

 young rotifers move their trochal discs along the needle. Whether 

 they will settle down and establish a colony seems to depend 

 chiefly on food conditions. If the stem possesses but little debris 

 the ball may move along it for some distance, but in most cases 

 finally swims away. If, however, the stem has more debris 

 attached to it the young rotifers persist in their efforts to place 

 their trochal discs on this, probably in order to get the food par- 

 ticles. In this way the ball is prevented from moving away. If 

 the ball remains in one place for a time, one or two of the rotifers 

 will be seen dragging themselves out of the ball and moving 

 slowly along the stem. In this manner they move a short dis- 

 tance and then jerk back, then start out again, each time going 

 a little farther. Soon others come out of the ball and begin 

 moving about, until a large number are found moving up and 

 down the stem (Fig. 2). In moving along the plant the ani- 

 mals extend their bodies with the long axis parallel to that of 

 the stem. A few of the cilia of the trochal disc and a few of 

 those in the posterior circle appear to touch the stem and in this 

 manner the animals " crawl " along the plant, reminding one very 

 much of a brood of young caterpillars. But it is probable that 

 the water currents are here as at other times the most effective 

 agents of locomotion. In these movements there is no revolution 

 on the long axis. In advancing along the stem the animal 

 usually shows great hesitation in going over portions which have 

 not been traversed by some member of the colony. In the space 

 over which several rotifers have travelled others move with little 

 hesitation, but on coming to new territory they move forward a 



