108 CLAUDE W. MITCHELL 



vented and in accord with this the results show some irregularity. 

 Additional evidence, however, has been accumulated in the 

 course of the pedigree series. In many instances in these series 

 other than the first individuals have necessarily been used be- 

 cause of the phenomenon above noted, that the first members 

 of ill-fed families seemed peculiarly lacking in vitality. These 

 enforced shiftings of the sisters used for the pedigree families are 

 responsible for some of the slight irregularities in result shown 

 in table 1 and chart 1. 



New cultures 



After the cultivation of numerous lines of the saccate As- 

 planchna for three-and-a-half months, and, obtaining, in some 

 instances, nearly forty generations without a single transition 

 to the humped form, it was thought that possibly the strain of 

 rotifer used was somehow unsatisfactory, due, perhaps, to initial 

 weakness or to something artificial in the treatment of the initial 

 stock of resting eggs. These eggs had rested for but a very brief 

 period before hatching and had also been neither frozen nor dried, 

 processes which are probably typical in nature. It was deemed 

 best therefore, to start new lines from eggs freshly collected in 

 January at the borders of ponds where it was known the species 

 had flourished and where it was known that at least a portion of 

 these eggs had been subjected to both freezing and drouth. 

 No difficulty was experienced in hatching young AsplaAchna 

 from such material; many had emerged within five days after 

 adding tap water. The precaution was taken, however, of 

 hatching single individuals only from small portions of the debris 

 in order to assure the starting of series from the first generation. 

 Twenty-four such individuals were isolated, twenty-two of which 

 were allowed to reproduce in as many mass cultures, while the 

 other two were made the parents of series E and F. The his- 

 tories of the twenty-two mass cultures are given in table 7. 



Reference to the table will show that the results are conflicting; 

 in ten cultures humped individuals were developed, while in 

 twelve there were saccates on'ly. The conflicting results were 

 without explanation, although it was recorded in every case 



