March, 1916.] CrAMPTON : OrIGIN OF WiNGS. 13 



gill origin of the wings are apparently very forceful, and it must be 

 admitted that they exert a subtly fascinating appeal ; but there are 

 certain seemingly insurmountable objections to the acceptance of the 

 tracheal-gill hypothesis, as will be pointed out in the following dis- 

 cussion of the paranotal theory. The paranotal theory, on the other 

 hand, is not open to these objections, and is even more in accord with 

 the observed facts, as will be shown later, so that for the present, at 

 least, it is the more probable and acceptable theory. 



The principal points in favor of the paranotal origin of the wings, 

 and the objections to the tracheal-gill theory may be briefly reviewed 

 as follows : j 



1. Since the successive segments of an insect's body are mutually 

 homologous, we should expect to find structures homologous with the 

 wings, on the other segments. Now in order to derive the wings 

 from such structures, it must be shown that they are homologous with 

 them, and in order to be homologous with the wings, these structures 

 must be homodynamous (?. c, of the same developmental series) with 

 the wings — otherwise, it would be impossible to derive the wings 

 from them. If then, it can be shown that the wings are not homo- 

 dynamous with the tracheal gills, the theory that the wings are modi- 

 fied tracheal gills immediately becomes untenable. 



In his embryological studies of Ephemerids, Sialids, etc., Hey- 

 mons (1896) has clearly demonstrated that wings do not arise simi- 

 larly to tracheal gills, and that the tracheal gills are not homody- 

 namous with the wings — and these investigations alone, are sufficient 

 to entirely refute the tracheal gill theory of the origin of the wings! 

 Furthermore, Heymon's conclusions based upon the embryology of 

 the Ephemerid?e, etc., are fully borne out by the work of Duerken 

 (1907) who has shown that the structure and musculature of the gills 

 of Ephemerids are not comparable to those of the wings, and Boer- 

 ner's (1909) studies on the tracheal gills of Ephemerids have shown 

 that the gills are not homodynamous with the wings. Indeed, as 

 Fernald (1890) and others have pointed out, the gills may occur in 

 various localities, and even between the wings, so that under these 

 conditions, it is not surprising that embryological and anatomical in- 

 vestigations have demonstrated that the gills are not homodynamous 

 with the wings. 



2. If it could be shown that, in certain immature Ephemerids 



