184 FRANK M. SURFACE. 



young animal finally bursts the enveloping membrane and is 

 able to swim about. The young rotifers possess an organization 

 in most respects similar to the adult. But among the more im- 

 portant differences maybe mentioned the following. The trochal 

 disc is at this time no broader than the trunk, the whole animal 

 tapering slightly towards the foot. At the foot there is a circlet 

 of small cilia. On the anterior border of the trochal disc, near 

 the dorsal side are two red eye spots which are lacking in the 

 adult. The cement gland in the foot is proportionately larger 

 in the young animal than in the adult. 



The young rotifers are free swimming, but are always attached 

 at the posterior end by a thread of adhesive material which they 

 spin out much after the fashion of a spider. They swim about 

 among the adult rotifers, sometimes venturing a short distance 

 beyond the limits of the colony but always drawing back and con- 

 tinuing to move about among the old animals. During all this 

 time they are attached to the old colony by the adhesive thread 

 from the foot. By a continuation of this nervous crawling and 

 swimming some of them finally get their webs so twisted together 

 that they are brought into contact. Here they remain, apparently 

 without secreting more of the adhesive thread. At first there 

 are only two or three individuals thus approximated and these 

 are near the center of the old colony. Soon other young rotifers 

 get their webs entangled with that of the few aggregated ones 

 and these are then added to the ball that is forming. Here as 

 well as later, contact with the adhesive thread appears to act as a 

 guiding stimulus to the young rotifers. As soon as a young 

 animal comes in contact with the rather thick thread leading to 

 the forming ball, it at once begins to move up or down this 

 thread until it finally reaches the ball ; this I have repeatedly 

 seen. Usually the young animal does not at once attach itself 

 to the ball, but continues to crawl about, often through the 

 bunch of young rotifers. In this way it finally becomes attached 

 to its comrades with its foot closely adhering to theirs. During 

 all the time that the ball is forming, the individuals composing it 

 act in a very nervous manner, constantly jerking, twisting, con- 

 tracting and expanding in a most irregular way. By means of 

 this continual twisting and squirming the forming ball succeeds 



