FORMATION OF NEW COLONIES OF MEGALOTROCHA. 191 



gradually waste away, it seems possible that they may function 

 in the same manner as the leucocytes of many other animals. 

 After the eye spots have disappeared from their original location 

 the animals no longer react to light. 



GENERAL AND COMPARATIVE. 



The main features in the formation of new colonies of this 

 rotifer are then as follows : When first hatched from the eggs 

 the young are free swimming, but do not leave the colony singly. 

 These individuals come together into a swimming ball which re- 

 acts positively to light. Later under certain conditions this 

 breaks up into free individuals again. These then aggregate 

 themselves into a permanent colony in which the animals spend 

 the remainder of their lives. In this colony formation the 

 mucus-like secretion of the foot-gland plays an essential part. 



The details of colony formation in other rotifers has appar- 

 ently not been described, but it seems probable from the known 

 facts that a similar sequence of processes occurs in some other 

 cases. In Ladnularia socialis according to Huxley ('53), Hud- 

 son and Gosse ('89) and others, the process appears to resemble 

 that in Mcgalotrocha. The young animals come together into 

 swarms or balls and swim freely. Later permanent colonies are 

 found on water plants. In two species of Meg.alotrocha from 

 China, i'iz., M. semibullata and M. spinosa described by Thorpe 

 ('89 and '93), the adult colonies are free swimming. In these 

 cases the eye spots are present in the adults. The new colonies 

 swarm out of the old free swimming ones. Occasionally these 

 balls may be found suspended from aquatic plants by mucilagi- 

 nous threads. In the genus Conochilus we find swimming colonies 

 of a slightly different nature. Here the free swimming balls con- 

 sist of several adults with many of their young. According to 

 Hudson and Gosse many of the newly hatched rotifers make a 

 place for themselves in the adult ball by squeezing between the 

 older members, while others of the new brood form new balls 

 and swim away. There are several other more or less rare 

 species of Melicertidae in which free swimming or fixed colonies 

 have been described. The free swimming adult colonies are in- 



tZ> 



teresting as apparently marking a step in the formation of the 



