No. 549] A CASE OF POLYMORPHISM 



551 



It is worth noting— though this is in part but restating 

 the last thought in different language— that the varia- 

 tions here described differ from the majority of those re- 

 cently recorded for minor invertebrates;" lor example, 

 the modifications in Daphnia, Uosmiim, and Asplmich no , 

 so carefully observed by "Wesenberg-Lund. These latter 

 variations are in the main variations in external form 

 only, and seemed to be pure reactions to external con- 

 ditions, taking place, for example, when the surrounding 

 medium has reached a certain temperature, and again 

 lapsing very soon after the temperature has dropped. 

 Such variations fall naturally under the rubrics o! sea 

 sonal polymorphism, temporal variation, or cyclomorpho- 

 sis. The variations which we have studied in Asplanchna 

 refuse to be thus classified. 



It is true that the stability of these variants is mark- 

 edly different, being greatest for the humped type and 

 least for the minor saccate form, but a stability that 

 tends strongly to resist external influences is none the 

 less obvious for each. And this seems to the writer to 

 render it highly probable that each of these variations is 

 of germinal origin. If this is the case it is the more 

 striking that this germinal variation is itself a variable 

 and elastic quantity, originally initiated by nutritive 



variations do occur in a rhythmic or cyclical fashion, in 

 that, namely, each form may produce a fertilized or rest- 



through the restin 

 genetic ova. It is 

 there is complete 

 hatched from resti 

 already been made 

 resting eggs of th 



