TRANSITIONS IN MORPHOLOGICAL CHARACTERS 119 



gives the history of D to its one-hundredth generation, at which 

 point the records were discontinued though the series was con- 

 tinued for a number of generations before discarding. 



Observations on mutations occurring in mass cultures fed on Moina 



In a large mass culture, into which all discarded A. amphora 

 were thrown, the crustacean Moina parodoxa developed. Some 

 of the Asplanchna succeeded in ingesting the young Moina despite 

 their large size. This diet was followed by a mutation to the 

 humped type. Although it was not demonstrated by actual 

 observation that Moina feeding caused the transition in the cul- 

 ture, yet a few minor experiments not mentioned elsewhere in 

 this paper, in which this type of food was employed proved con- 

 clusively that this food change is also capable of producing the 

 transition. There resulted an interesting selection: a few of the 

 smaller humped rotifers and many of the saccates were unable to 

 capture and ingest the crustacean and as the amount of food de- 

 creased, died. The average size of the individual of the culture 

 was consequently increased. A period of male production fol- 

 lowed, with resting eggs. This again lessened the number of 

 individuals in the culture, and as the Moina also decreased in 

 number it finally died out. 



Observation on mutations occurring in 7nass cultures where Hydatina 

 and Brachionus were present 



To a number of ordinary mass cultures, fed as usual on Para- 

 mecium, the rotifers, Hydatina senta, Brachionus bakeri, and B. 

 urceolaris were introduced. The Asplanchna, after a time only, 

 began to eat these smaller rotifers and, as in the former experi- 

 ments with Euglena, the customary mutation occurred, and males 

 were produced followed by large numbers of resting eggs. These 

 two smaller rotifers furnished a more regular and lasting food 

 supply than did Moina and the cultures were continued for some 

 time, the humped type remaining constant throughout, with the 

 exception of a few individuals of the third type of the species. 



