Phylctic Parallelism in Aft tamorpkic Species. 463 



species would thus appear to be more nearly re- 

 lated than their larvae. 



Now this strained explanation is eminently in- 

 applicable to varieties, still less to species, and 

 least of all to higher systematic groups, for the 

 simple reason that every wave of transformation 

 may be assumed to be at the most of such strength 

 as to produce a deviation of form equal to that of 

 a variety. Were the change resulting from a sin- 

 gle disturbance greater, we should not only find 

 one-sided varieties, i. e. those belonging to one 

 stage, but we should also meet as frequently with 

 one-sided species. If, however, a wave of trans- 

 formation can only produce a variety even in the 

 case of greatest form-divergence, the above hypo- 

 thetical uncontemporaneous action of such a wave 

 in two species could only give rise to such small 

 differences in the two stages that we could but 

 designate them as varieties. An accumulation of 

 the results of the action of several successive 

 waves passing over the same species could not 

 happen, because the distance from a neighbouring 

 species would always become the same in two 

 stages as soon as one wave had ended its course. 

 In this manner there could therefore only arise 

 divergences of the value of varieties, and incon- 

 gruences in systematic groups of a higher rank 

 could not thus be explained. 



All explanations of the second form of incon- 

 grucnce from the point of view of a phyletic force 



