360 THE AMERICAN NATURALIST. [Vor. XXXV. 
to the wing, as suggested by Cholodkowsky ('86), or to the ptery- 
godum (tegula), the view adopted by Haase (86) and now so 
generally accepted. It should be observed, nevertheless, that 
the reasons given by Haase for reaching such a conclusion 
are far from adequate, since the only evidence to which he 
called attention, otherwise than a superficial resemblance, was 
that (1) chitinous folds of a similar nature but of secondary 
origin are present on the prothorax of certain Hymenoptera 
and Diptera, while (2) the patagia do not exist during the 
larval stage of the Lepidoptera, but commence their develop- 
ment in the first few days of the chrysalid stage. Unfortu- 
nately, however, Haase failed to demonstrate any homologous 
structures in the Hymenoptera or Dip- 
tera, and had he attempted to do so it is 
evident, from the preceding, that proof 
of their secondary nature would have 
been difficult to establish. Moreover, 
the Anlage of a structure must exist 
in potentio, and the time during the post- 
embryonic stages at which it commences 
that which is known as development can 
rc qu ids alone be of no particular value in deter- 
relations of pterygodum, wing, mining its palingenetic or cenogenetic 
episternum, and epimeron in 
the thoracic segment of the Character. The question as to whether 
Ta Pot References as in the patagium represents a prothoracic 
pterygodum or a wing, must await a large 
amount of comparative work based on embryology, with the 
possibility of paleontological’ evidence affording some help 
in the solution of the problem. The ratio of develop- 
ment between wing and pterygodum on the other thoracic 
segments allows the inference, however, that pterygoda may 
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ondon) suggested. Brongiart has already pointed this out. (Note sur quelque 
insectes fossiles du terrain houiller qui presentent au prothorax des appendices 
aliformes, Bull. Soc. Philom., tome ii, 1890.) 
