March, 1916.] CrAMPTON : ORIGIN OF WiNGS. 5 



In support of his contention, Plateau (1871) cites a number of 

 observations, which are, unfortunately, incorrect; and, since his prem- 

 ises are unsound, his conclusions are naturally false also. Thus, he 

 points out that Blanchard (1868), quoting De Blainville, states that 

 no respiratory orifice, or spiracle, is ever found in either the meso- 

 thorax or metathorax, and concludes that this absence of respiratory 

 orifices in the segments which bear, or should bear, the wings, gives 

 weight to the hypothesis (long prevalent even in Blanchard's day) 

 that the wings are largely composed of outgrowing trachese which 

 have become imprisoned between two integumental lamellae — a theory 

 accepted by Girard, and many others. 



As a matter of fact, the mesothorax and metathorax (i. e., the 

 wing-bearing segments) are usually the only thoracic segments sup- 

 plied with spiracles, which were either overlooked by the earlier in- 

 vestigators, or were ascribed to the wrong segment, due to the fact 

 that it was not then known that the thoracic spiracles might migrate 

 (during ontogenetic development) from the segment in which they 

 were formed during embryological development, and, taking up a po- 

 sition in the intersegmental region, appear to belong to the segment 

 in front rather than to the segment behind them. 



Plateau goes on to say that it is a significant fact that the wing is 

 always located between the epimeron and the tergum, which he thinks 

 is the typical situation of the spiracle. The thoracic spiracles of 

 adult insects, however, almost invariably occur in the intersegmental 

 membrane, or occupy an intersegmental position so that Palmen's 

 premises and conclusions in these matters are wholly incorrect. 



Plateau's conception of the wing as an hypertrophied spiracle 

 which has become widened and flattened to form the wing lamellae, 

 while the "supporting rods" (tsenidia ?) of the trachea become en- 

 larged to form the wing nervures, is entirely fanciful, as is his idea 

 that the halteres of the Diptera (which he rightly identifies as modi- 

 fied wings) are modified spiracles. Indeed, the only semblance of 

 proof offered by him in support of his theory, is in the observations 

 of Weismann (1866) which he cites, pointing out that Weismann's 

 investigations concerning the development of Corethra would indicate 

 that in this insect, the dorsal prothoracic cell-islands, or '' imaginal 

 disks," form the pupal spiracles, while those of the mesothorax form 

 the wings, and those of the metathorax form the halteres. It is by 



