350 C. W. MITCHELL AND J. H. POWERS 



The intitial mass culture thus derived proved remarkably 

 strong. By October 10, but three days after the isolation of the 

 single progenitor, hundreds of rotifers were present. Males 

 were also first seen on October 10, and the following day individ- 

 uals containing resting eggs were present. 



From this mass culture derived, as we have seen, from a single 

 individual, four series, in two contrasting groups, were started as 

 follows: First, one of the above-mentioned individuals containing 

 resting eggs was isolated on October 11, Its eggs, dropped two 

 or three days later, were placed in watch glasses containing fresh 

 tap water, where they began to hatch by October 24. Two of 

 these young were chosen to become the parents of series H and 7, 

 which, being similarly derived, constitute one group. Other 

 sister eggs hatched and were used to found general mass cultures 

 serving no other purpose than as subsidiary controls. 



Second, another group of two series was started in a different 

 way. The general mass culture from which the original pro- 

 genitor of H and I had been chosen was fed in a special manner 

 so as greatly to increase its numbers, to induce cannibalism, and 

 thereby produce a number of the third or campanulate type of the 

 species. These campanulates were active cannibals in their own 

 culture before their isolation. After isolation they were fed 

 upon numbers of the saccate form of their own species. Male 

 production soon followed. As soon as this was noted a single 

 young campanulate was isolated and fertilized by a large male 

 produced by another campanulate mother; resting eggs were pro- 

 duced, and after suitable treatment began to hatch on December 

 2. Two of these young were used to become the direct progeni- 

 tors of the two series J and K. 



The relation of the above-mentioned four series should thus be 

 clear: All are the descendents of one parthenogenetic female 

 although many generations removed. H and I are derived from 

 individuals which are full sisters hatched from resting eggs pro- 

 duced by the humped type. J and K are likewise full sisters but 

 hatched from fertilized eggs derived from the still higher or 

 campanulate stock. Thus the immediate progenitors of these 



