166 THE SHORTER SCIENTIFIC PAPERS 



in connection with a footnote attached by Audouin to a 

 translation of a paper by MacLeay (1832), where Au- 

 douin suggested that the piece termed the squamula in 

 the Hymenoptera was homologous to the parapteron, 

 which he had noted in Dytisctcs. Consequently, the term 

 parapteron really has no standing. 



The patagium of the prothorax corresponds, I am in- 

 clined to believe, to the mesothoracic and metathoracic 

 wing, and similarly possesses a propteron. To one famil- 

 iar with the embryos of certain of the termites as well as 

 with the structure of the prothorax in many fossil insects, 

 the reasons for such a conclusion will seem obvious. 



The problem of the origin of the wings still remains a 

 difficult one. That they do not correspond to the tracheal 

 gills seems certain, particularly when one takes into con- 

 sideration the relative position of the gills, the coxoster- 

 num, the pleurites and the metathoracic coxae in a young 

 Ephemerid. The presence of the episternal and epimeral 

 areas, assuming that the parapodium furnishes an inter- 

 pretation of the origin of the pleurum, might lead to the 

 assumption that a basal notopodial as well as a basal neuro- 

 podial cirrus had become changed into an elytral scale- 

 like formation receiving tracheal branches and had given 

 rise to the wing and propteron. The structure of Worth- 

 enella cambria Walcott, a middle Cambrian annelid with 

 the apparent biannulate division of the segments as sub- 

 sequently figured (Fig. 4), is interesting in this connec- 

 tion. The theory of the origin of the wings, as proposed 

 by Miiller (1875), namely, that they are developed from 

 the expansion of the tergum, seems to be untenable, al- 

 though it is the one which has generally been accepted. 

 Nature has a tendency in evolution to modify existing 

 organs rather than to develop new structures, and I would 

 here consider such a tergal expansion with its new articu- 

 lation and wing muscles a new structure. 



The position of the spiracular openings on the anterior 

 margin of the segment is quite consistent with the para- 

 podial development of the pleurum in that the scattered 

 respiratory pockets of the integument, reduced in number 

 to the paired segmental spiracles with their ramifying 



