VAKIATION AND ABERRATION IN BUTTERFLIES. 14? 



within the limits of its variation as observable at the present 

 day, while another species far transcends those limits, the answer 

 may be given as follows : that those species which have already 

 existed on the earth for very long periods of time either under 

 their present aspect or under one very closely resembling it — in 

 short, the phylogenetically older species — come under the first 

 category; on the other hand, those species that have_ only 

 possessed their present aspect for a considerably shorter time — 

 that is, the phylogenetically younger species — belong to the 

 second category. 



To demonstrate the high probability of this supposition would 

 lead us too far from our present subject. 



I must not omit to mention that the modifications induced by 

 these experiments cannot all be classed under the four headings 

 so far given ; there is, in fact, a small unexplained residue, con- 

 stituting a fifth group, which possibly represents the completely 

 independent reaction of the individual species, uncontrolled by 

 any inherited developmental tendency, to the influences brought 

 to bear upon it. We must not forget that agents were employed 

 that in nature never, or only most exceptionally, operate upon 

 these creatures with such intensity. Still, as the short span of 

 human life does not allow any one man to expose methodically 

 for successive centuries (which alone would give any prospect of 

 results) generation after generation of such creatures as are 

 suitable for experiments of this kind to conditions which may be 

 expected to have an effective influence, and which are actually to 

 be met with here and there upon the earth, the only course that 

 remains open for the experimenter is to intensify the conditions 

 which determine the changes of the organic world, and to take 

 the sum of the series instead of the terms of the series at length. 



As above stated, I had already in 1892 (Entom. Zeitschr., 

 Guben, Dec. 1st, 1892) clearly hinted at the phylogenetic 

 character of one of these forms, and had then signified my in- 

 tention of publishing further details at the earliest opportunity. 



This explanation of the forms now in question has perhaps 

 been offered for the first time in all entomological literature by 

 mj'self. 



In order to avoid reasoning from inadequate data, and other 

 forms of error, which are only too apt to be induced by accidental 

 peculiarities of the material subjected to experiment, or by per- 

 forming the experiments on an insufficient number of species, I 

 have during the last few years tested the influence of temperature 

 on over 5000 pupEe — 3000 or so in the present year alone. _ 



It was proved in the course of this work that experiments 

 with raised temperatures were very difficult, since the great num- 

 ber of species hitherto tested showed themselves to possess small 

 powers of resistance to high degrees of warmth (40° C, 104" F., 

 rapidly caused death in almost all species, P. viadiaon and F» 



