358 THE AMERICAN NATURALIST. (VoL. XXXV. 
the various components of each being reduplicated in the 
other segments, subject, however, to the factors governing the 
specialization of the different groups of insects, the existence 
of a corresponding piece in the metathorax would a priori 
be inferred. The presence of such a piece! is represented 
in the accompanying diagram (Fig. 2), while a homologous 
part can generaly be demonstrated throughout the other 
orders (Figs. 3, 4). Furthermore, it is to be noted that in the 
typical form this is joined to the dorsal 
margin of the episternum, while the wing 
is articulated with the dorsal margin of the 
epimeron and not, as hitherto accepted, with 
the episternum.? 
In connection with the facts noted above, 
certain evidence is available, based on em- 
bryology as well as comparative anatomy, 
which adds weight to the inference that 
Fic. 2.—Cossus ligni- these two pieces are rudimentary? wings 
erda. Left lateral $ 
portion of metathorax, aNd that the thorax of the Hexapoda is com- 
oe: Doar sci in posed of six somites which in the typical form 
bear the fundaments of six pairs of wings. 
The development of the mesothoracic pterygodum* (=tegula, 
parapteron, etc.) is of extreme interest in this connection and 
furnishes interesting evidence toward establishing the hypoth- 
esis I have put forward regarding its relation to the wing. 
This, however, is only one of a large number of facts which 
corroborate such a view and which appear explainable on no 
1 From comparisons made throughout the Hexapoda it is evident that this 
does not correspond to the more or less chitinized part of the epimeron at the 
base of the wing in most Lepidoptera. 
The anterior margin of the wing is generally specialized at the base, so that 
it partially extends over the dorsal portion of the episternum, while an articula- 
tive process of the pterygodum may be received into a corresponding notch of 
wing. (See Fig. 3) This condition, however, is secondary. A 
here appears to be no evidence for regarding these as vestigial, since it ng 
improbable that forms with six pairs of wings ever existed. The term “ rudi- 
mentary,” as generally used, does not seem inappropriate, although the quc 
* fundament" is more concise. 
*Owing to its greater size, this can be more conveniently studied than the 
Corresponding piece on the metathorax. 
