1895.] The Classification of the Lepidoptera. 253 
cephalization of the flight function, manifested by a reduction 
of the hind wings and a specialization of the fore wings as 
strongly supported firm plates for rapidly beating the air ob- 
tained. This synchronity of action by the two pairs of wings 
and the cephalization of the fight function, was accompanied 
by coincident structural changes in the segments containing 
the wing musculature. . With the loss of independence by the 
two pairs of wings, and the development of their united action, 
the meso- and metathoraces became more and more combined 
until in some cases they are so nearly fused as to form a single 
strong box for the wing musculature. The cephalization of 
‘flight or the reduction of the hind wings and the specialization 
of the fore wings is accompanied by a corresponding reduction 
in size and importance of the metathorax, and a marked in- 
crease in size of the mesothorax. 
The musculature of the legs is also, of course, contained in 
the thoracic segments, but where, as in the Lepidoptera, the 
functions of the legs are so largely reduced, so overshadowed 
by the flight function that the anatomy of the thorax depends 
almost entirely on the specialization of the wings, and where, 
as is also the case in the Lepidoptera, the flight function and 
consequent condition of the wings is of somuch ‘importance in 
the economy of the organisms, it is evident that the testimony 
borne by the thoracic anatomy should be a contribution of 
real importance towards a comprehension of the phylogeny of 
the group. 
Asa fair example of the lepidopterous thorax in a species 
certainly not among the more highly specialized Lepidoptera, 
and admittedly not belonging to the most generalized forms, 
I have taken the thorax of Actias luna. As our interest lies in 
the meso- and metasegments, being the ones directly connected 
with the function of flight, I may omit reference to the pro- 
thorax. 
The scutum of the mesothorax in luna (See fig. 2, plate 
XVII) is the largest sclerite of the dorsum, and presents a 
greater surface than all the rest of the dorsal sclerites of the meso- 
and metathorax combined. It is longer than broad, is traversed 
‘T See Comstock, Joc. cit., p. 51. 
