INDUCED CHARACTERS IN ASPLANCHNA AMPHORA 349 



lized egg, so it is readily conceivable that in the parthenogenetic 

 series of rotifers the tendency for certain form-changes to occur 

 in generations more or less removed from the resting egg maj^ none 

 the less have been determined by the nature of that egg as such. 

 In short, there may be hereditary. Or, to put the same thing in a 

 different way for clearness, it is conceivable that inheritance 

 through the resting or fertilized egg of this rotifer need not mani- 

 fest itself in the visible characters of the individual which emerges 

 from this egg; it may be hidden as tendencies only to manifest 

 itself in later generations. 



A few terms may be briefly defined as an aid to readers not 

 familiar with our preceding studies upon Asplanchna. A pedi- 

 gree-series is a succession of individuals derived, by partheno- 

 genetic reproduction, from a single resting or fertilized egg. One 

 of the early members of each generation is usually isolated to 

 become the parent of the succeeding generation. The term meta- 

 bolic rhythm has been used to indicate an internal rhythm which 

 can be measured by the rise and fall in the number of young born, 

 under normal conditions, to the individuals constituting the 

 generations in the pedigree series. The words, type, form, and 

 stage, refer to the tri-morphic conditions in which this rotifer is 

 found. The word potential is used to indicate the different phys- 

 iological levels as represented by these three different stages. 



EXPERIMENTS 



All the Asplanchna employed in the following experiments were 

 derived from stock used in the previous year in the studies upon 

 sex-determination. A single mass culture had been carried 

 through the summer. Four healthy individuals were chosen 

 from this in the fall and were tested by allowing them to multiply 

 rapidly in a single mass culture. The stock seemed good: In 

 a few days many had been born and even males had been pro- 

 duced. On October 7 a single individual was cho.sen to become 

 the parent of the mass cultures from which all series and cultures 

 used through the experiments were derived, all other material 

 being entirely discarded. 



