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



271 



In this connection it may be stated that the Apteryguta are no 

 more to be regarded as degenerate Pterjgota, than Amphioxus is to 

 be regarded as a vertebrate; and the fact that certain highly specialized 

 {or even degenerate) features may be found in any otherwise very 

 primitive organism throughout the animal kingdom, should surely be 

 known to those who claim that all apterygote insects are degenerate 

 forms. Furthermore, the remarkable similarities of structure in the 

 more primitive members of the apterygote and pterygote insects are 

 too profound and far-reaching to be explained merely as the result of 

 -a parallelism, or a convergence of development in the two groiips. 



From the foregoing facts, it would seem reasonable to regard 

 tke more primitive members of the Apterygota as the nearest living 

 representatives of the ancestors of the Pterygota — that is to bay, they 

 have change the least from the original ancestral condition — and 

 a comparative study of the insects belonging to the various groups 

 included in the lines of descent described above, will furnish valuable 

 €lues as to the derivation of Pterygota from wingless ancestors. 



It has been already pointed out that there are several separate 

 and distinct lines of development leading from the apterygote forms to 

 the winged insects. On this account, there is no force to the objection 

 raised to the Dicelluro-Dermaptera line of descent on the ground that 

 the more primitive types of fore wings, the segmented caudal appen- 

 •dages, etc., of other winged insects, could not be derived from the 

 hightly specialized fore wings, forceps-like caudal appendages, etc., of 

 the earwigs; for if there are several lines of descent from the Aptery- 

 gota to the Pterygota, it is self-evident that all other winged insects 

 were not derived from the Japyx-like forms through the earwigs, as 

 this objection would imply. 



The Japyx-like forms were themselves derived from ancestors 

 liaving segmented caudal appendages instead of forceps — an ancestral 

 Kondition which has been retained in such Dicellura as Projapyx. On 

 this account the occurrence of segmented caudal appendages in the 

 immature stages of certain Dermaptera (such as Dyscritina) is to be 

 regarded as a case of „atavism", and the same may be said of similar 

 structures in the Coleoptera larvae. It is merely to be expected that 

 immature forms would retain certain primitive characters, even though 

 these were lost in the adult condition, since this state of affairs occurs 

 •everywhere in animal kingdom. Instead of being an argument against 

 the Dicelluro-Dermaptera line of descent, the fact of the presence of 

 segmented caudal appendages in certain immature Dermaptera would 

 therefore seem rather to be an argument in favor of it. 



Allowing for differences of adaptation in the two groups, it would 

 be an easy matter to derive the trophi and thoracic structures of the 

 Dicellura and Dermaptera from a common ancestral type, and the 

 marked similarity between the caudal appendages of the two groups, 

 is too profound to be laid to coincidence. The logical inference then, 

 is that they sprang from a common ancestry. 



Closely allied to the Dicelluro-Dermaptera line, is the Dicelluro- 

 Coleoptera line, leading from the Japyx-like forms to the Coleoptera. 

 The similarity in structure between certain of the Dicellura and the 

 larvae of such beetles as Cucujus and Pyroclwoa is so striking, that it 



