178 
Psyche 
[December 
from the ancestral Holometabolous stock, which was prob- 
ably a Protorthopteran type with body structures like those 
of primitive Isoptera and Embiids, and with a venation re- 
sembling that of certain Protoblattids. Handlirsch would 
derive the Mecoptera from Megasecoptera, but the Megase- 
coptera belong in the section Palseopterygota, whose mem- 
bers are incapable of laying the wings back along the body 
in repose, while the Mecoptera are clearly Neopterygota 
capable of laying the wings back along the body in repose, 
and the resemblance between the venation of certain 
Mecoptera and Megasecoptera is apparently the result of 
convergence. 
The Diptera were undoubtedly descended from Mecoptera- 
like forebears, as is evidenced by all of their structural 
features; and fossils such as Aristopsyche (called Paratri- 
choptera or Protodiptera) , which have a venation strikingly 
suggestive of the ancestors of the Diptera, merge so indis- 
tinguishably with the Mecoptera, that it is very doubtful 
that they are worthy of ordinal rank, and it is preferable to 
group them with the Mecoptera as a suborder of Mecoptera. 
Among the living Mecoptera, such forms as Nannochorista 
have preserved numerous features suggestive of the ances- 
tors of the Diptera , 2 and clearly indicate that the labella of 
Diptera, for example, are merely modified segments of the 
labial palpi. 
The Trichoptera have likewise preserved a great number 
of characters strikingly suggestive of the precursors of the 
Diptera, but the Trichoptera are more closely allied to 
the Lepidoptera than any other insects. In fact, the 
Rhyacophilid Trichoptera merge so indistinguishably with 
the Micropterygid Lepidoptera that it is very doubtful if 
the two groups are worthy of ordinal rank, although it is 
preferable to treat them as distinct orders for the sake of 
convenience. Fossils such as Belmontia (usually placed in 
a distinct order the Paramecoptera or Prototriehoptera) 
are strikingly suggestive of the common ancestors of the 
Trichoptera and Lepidoptera and lead back to ancestors 
2 The Tanyderidae and Trichoceridae are the most primitive living 
Diptera, and the Anisopodidae are very like the ancestors of the 
Brachycera, whose most primitive representatives are the Therevidae 
and Rhagionidae (Leptidae), while the Syrphidae have departed but 
little from the ancestors of the Cyclorrhapha. 
