270 



Notes on the derivation of winged insects through several lines etc. 



gota. Closely associated with the Dicelluro-Dermaptera line, is the 

 DiceUuro-Coleoptera line, leading from the Japyx-like forn:is to the 

 Coleoptera. 



Certain points of similarity between the Thysanura (as repre- 

 sented by Lepisma and Machiiis) and the my-flies, or Ephemeroidea, 

 suggest that there may have been a Thysanuro-Ephenieroidea line of 

 descent from the Apterygota to the Pterygota, in addition to the other 

 lines mentioned above. Furthermore^ it is extremely probable that 

 a farther study of the more primitive representatives of the Apterygota 

 and the Pterj^gota, and the bringing to light to new forms (such as 

 the recently discovered Myrientomata) will disclose still other lines of 

 descent leading from the primitively wingless to the winged insects, so 

 that the group Pterygota may be considered as in a sence a „poly- 

 phyletic" one. 



It is quite obvious that recent pterygote insects cannot be the 

 descendents of apterygote forms now living, since both groups have 

 diverged from the common stem, and the various members of the two 

 groups have followed their own lines of development, some becoming 

 more profoundly modified than others. On the other band, it is equally 

 true that a few representatives of each group, although modified in 

 some respects, have nevertheless retained certain very primitive 

 characters, which are of great phylogenetic value in tracing the ancestry 

 of the two groups — a point which is not given sufficient weight by those 

 who seek to discredit all attempts to derive the Pterygota from ancestors 

 similar to the apterygote forms. 



As an objection to the theory of the descent of the Pterygota 

 from apterygote forms, it has been stated that certain branches of the 

 Apterygota have reached a higher degree of specialization, or have 

 become more profoundly modified; than the lover Pterygota; but I fail 

 to see wherein this has any bearing upon the fact that still other 

 branches of the Apterygota have remained in a remarkably primitive 

 condition. It is self-evident that an off-shoot from any group of 

 animals may become highly modified, or adapted in a certain direction, 

 while others of that group (usually few in number) may remain but 

 slightly changed from the ancestral type. If this were not true, the 

 evolutionists would have but little material to work upon! 



A somewhat similar objection raised by the opponents of this 

 theory, is that in certain particular features (e. g. the modified mouth- 

 parts) even the most primitive of the Apterygota may be more highly 

 specialized than the lower pterygote forms are, so far as these particular 

 features are concerned. This, however, should not outweigh the fact 

 that in other respects, the lower forms of the Apterygota are far more 

 primitive than the lover Pterygota, and have even retained certain 

 ancestral characters strongly suggestive of the Myriopoda. Throughout 

 the realm of Zoology, we find that animals which have retained certain 

 ver}^ primitive characters, may be highly specialized in other regards, 

 since all living ihings must adapt themselves in some respects at least, 

 to differences of environment. This fact is well illustrated by such 

 forms as Amphioxus, which is highly specialized in some respects, yet 

 this fact does not detract from the phylogenetic value of those very 

 primitive characters which it still retains. 



