PRESIDENT’S ADDRESS 335 
ence to the beautiful figures and descriptions in the work of Com- 
stock and Needham just mentioned will suffice. 
Granting, however, a common origin for the wings of all 
insects the problem of their original appearance, the factors in 
development become all the more interesting. In order to show 
the position taken by different students of the subject I beg to quote 
a few paragraphs from various sources. Gegenbaur presents the 
following: “The wings must be regarded as homologous with 
the lamellar tracheal gills, for they do not only agree with them 
in origin, but also in their connection with the body and in 
structure. In being limited to the second and third thoracic 
segments they point to a reduction in the number of the tracheal 
gills. It is quite clear that we must suppose that the wings did 
not arise as such, but were developed from organs which had 
another function, such as the tracheal gills; I mean to say that 
such a supposition is necessary, for we cannot imagine that the 
wings functioned as such in the lower stages of their development, 
and that they could have been developed by having such a 
function.” 
This general view is stated a little more in detail by Lang: “The 
problem of the phylogenetic origin of the wings of insects is extreme- 
ly difficult and as yet by no means solved. The rise of such organs 
is not explained by saying that they are integumental folds, which 
gradually increased in size, stood out from and eventually articu- 
lated with the body. The wings must in all stages of their 
phylogenetic development have performed definite functions, Tt is 
impossible that they were originally organs of flight. What 
function it was that they performed before they became exclusively 
organs of flight, is, however, entirely a matter of conjecture. The 
following view is at present the most acceptable. (1) The an- 
cestors of the Hexapoda were, like the now living Apterygota, 
wingless land animals breathing through tracheae. (2) The 
Apterygota-like ancestors of the Pterygotan racial group became 
adapted to living in the water. Dorsal integumental folds served 
for breathing in the water. The rise of such respiratory folds 
offers no difficulty, since every increase of surface, small or large, is 
of service. (3) The respiratory appendages (into which the trachea 
were continued) became movable and may perhaps have assisted in 
locomotion (swimming). This assumption also offers no difficulty, 
since the gills of many aquatic animals are movable, and their 
power of moving 1s an advantage on account of the exchange of 
water thus caused. (4) In a new gradual change to land life the 
respiratory function became less important and the locomotory 
function came to the front. Here, however, lies the greatest dif- 
ficulty. It may, however, be assumed that the animals, while still 
living in water were capable of gliding over the surface of the 
water by the swinging of their branchial leaves, just as flying fish 
