146 THE ENTOMOLOGIST. 



Examples of this, from the experiments above recounted, 

 are furnished by certain forms of T\ io, T. cardui, and Argynnis 

 aglaia. 



It is accordingly in a high degree probable that a large 

 number of the aberrations that occur in nature, of which the 

 immediate causes have hitherto seemed so strangely obscure and 

 incomprehensible, may have arisen by the influence of abnormal 

 temperature-conditions on the pupal stage. 



Nevertheless I should certainly not like to lay this down 

 even as a probable law controlling all aberrations. There are 

 undoubtedly a large number of aberrations which are not in any 

 way connected with the conditions of temperature which have 

 befallen the pupa. There is no reason at all why the special 

 aspect of the perfect insect should be exclusively the result of 

 antecedents belonging to the pupal condition. 



Fourthly, these experiments give rise to phylogenctic forms ; 

 forms, that is, which are nowhere to be found on the earth at the 

 present day within the compass of the species, but which may 

 either have existed in past epochs, or may perhaps be destined 

 to arise in future. 



The first, which may be called ** obsolete forms," show an 

 approximation of these to other species which are their nearest 

 relatives, and from whose ancestors they have been separated 

 during past ages. 



According to the above researches this separation resulted 

 probably from the operation of a constant increase or decrease of 

 temperature on the species in question during long periods of 

 time. Such an influence may have been brought to bear 

 through the modification of temperature-conditions having taken 

 place in the actual habitat of the species, or from the species 

 having migrated into a more southerly or northerly region. 

 From the material discussed above, I may adduce as examples 

 certain cooled forms of V. io and V. antiojm, and certain warmed 

 forms of V. atalanta. 



The second, i. e., possible forms of the future, are further 

 removed from the type of the related species, thus contrasting 

 with the first kind of " phylogenetic forms" (certain warmed 

 forms of T^ antiopa and certain cooled forms of V. atalanta). 



It is assuredly most remarkable that, as our experiments 

 show, the very same conditions will lead to the transformation 

 of one species into its varieties, and of another species, to some 

 extent, into forms that manifest a most striking approach to 

 those of other types. 



It is therefore impossible to adopt any fundamental distinction 

 between species and variety on the one hand, or between species 

 and species on the other. 



Should the question be asked, How does it happen that in the 

 foregoing experiments one species becomes transformed entirely 



