38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5

1

E.

Weinland

(Zeitschr. f. Wissens. Zool., li. pp. 55-166) lias con- cluded

from

his studies of the halteres that these organs are func- tional in determining the direction of flight.

They

can he used to steer a course in the vertical plane as well as in other directions, lie also concluded that the chordotonal structures in the hase of the halteres allow the perception of the steering

movements

of these organs.

But

it is highly probable that the great nerve trunk sup- plied to the halter is not primarily subservient to this dirigible func- tion, hut rather to that of audition, at least in the higher families.

In the

Nemocera

the halteres

may

be mainly dirigibleor equilibratory in function, since the auditor}' organs are located in the antenna?.

In the Cyclorrhapha, however, it

seems

safe to

assume

that their function is primarily auditory.

As Lowne

suggests, the halteres are doubtless

microphones

of a

most

efficient nature, capable of perceiv- ing sound

waves

of such low intensity that they

do

not affect the vertebrate car.

They

possess a function of coordination, similar to that of the semicircular canals of vertebrates,

and

thus arc organs

combining

the functions of equilibration

and

audition.

The

tegulse of the

Schizometopa and some

other Diptera are very likely functional in collecting sound-waves, increasing the perceptive

power

of the chordotonal organs of the halteres, thus being ana- logues of the external cartilaginous ear-lobes of the

mammalia.

They

also doubtless serve secondarily as a protection to the highly sensory halteres. It seems .safe to

assume

that in those dipterous groups having no tegular the halteres

perform

chiefly a function of equilibration, but that in those

groups

furnished with tegulse the hal- teres are mainly organs of audition. In other words, the presenceof well-developed tegulse indicate- the presence of a highly developed auditory sense in the halteres.

Mere

protection to the latter

would

not

demand

such structures as the tegulse, while it can not be denied that they arc admirably adapted to such a function as the collection ofsound-waves.

Whatever may

be ^finally determined as to their functions, it is

certain that the habere- are highly specialized organs.

The

tegulse, without doubt accessory tothem, are

by

inference equally functional

and

of coincident evolution with

some

function pertaining to them.

The

latter, therefore, can not be accepted as affording characters of value for the separation of large groups, but are rather of decidedly inferior rank in this respect to the veins of the wings.

They

occur

in other groups entirely outside of

and removed from

the Schizo- phora, and even

from

the Cyclorrhapha. Their presence in the

An-

thomyioidea is therefore not necessarily to be construed as indicating a close relationship

between

that superfamily and. the Muscoidea.

TAXONOMY

OF

MUSCOIDEAN FUHS — ToWXSEXD

₃₉

The

Acroceridae, for instance, are to be noted as an extra-cyclor-

rhaphous group which

has developed very large tegulae, wholly con- cealing the halteres

and

probably accessory to a highly developed auditory sense in the latter. It

seems

to be chiefly groups contain- ing a large percentage of endoparasitic

forms which

are provided with teguke.

and

it is possible that a greatly increased auditory per- ception is necessary to these

forms

as

an

aid to

them

in the search for

and

ultimate detection of their hosts.

The

validity of the time-honored separation of the Calypterata

and

Acalypterataonthecharacters of thecomparative presenceorabsence of tegulae alone

may

well be

open

to serious doubt.

The

unflexed fourth vein,

which from

its doubtless far greater age should be a nuich

more

valid character,

would

indicate a closer relationship of the

Anthomyioidea

with the Acalypterata than with the Muscoidea.

Yet this does not appear to be the proper

and

natural grouping. It rather seems preferable to adopt Brauer's

names Schizometopa and Holometopa

as

founded

on characters of greater valne than either those afforded by relative development of tegul?e or those of

wing

venation,

and

to recognize therefore the

Anthomyioidea

as a super- family of the Schizometopa.

While

the result is mainly the same, the divisions

become founded on

valid rather than on mutable char- acters.

The

tegul?e

have

developed,

though

not uniformly, in the Schizometopa.

They

have also developed to a certain extent in

some

of the

Holometopa.

This fact demonstrates their unfitness for

taxonomic

use inthese divisions.

There

is a distinction

between

the characters of a functional

organ and

the character of the presence or absenceofsuch organ.

Moreover,

it

may

be noted that Robineau- Desvoidy's division Calypteratae

was

applied

by him

to the super- family

Muscoidea

of the present paper in the

main

sense, as is

further brought out under the head of Synopses.

Abdomen. — The number

of abdominal sclerites should be of sub- family significance at least,

and

the

form

of the

abdomen

is almost invariably of generic value.

MacrochcetcE

and

bristles.

—

Chsetophorousness in the Diptera finds the climaxofits developmentin thetachinoid stock of the Muscoidea.

While

chaetophorous characters are, evolutionally, of recent origin, yet the

arrangement

of the macrochaetae of the head, thorax, abdo-

men, and

legs

becomes

highly important in separating tribes, genera,

and

species.

The

characters to be derived

from

the macrocha?ta? of the head rank even higher

and

serve for the separation of subfamilies in certain cases. In one or

two

groups, the

Gymnosomatinae and

Phasiina?, the peculiar chaetotactic characters of the head are cor- related with an absenceof macrochaetae on the

abdomen,

while in cer-

40 SMITHSONIAN MISCELLANEOUS COLLECTIONS

VOL. 51 tain other groups, as the Hystriciinae, a different type of

them

is

correlated with a true spinose

development

^{of the}

abdominal macro-

chaetae.

The

^cephalic bristles are uniformly present in the super- family,

though sometimes weakly

developed,

whether

the

abdominal

ones are present or absent.

The same

is usually true of those of the thorax

and

scutellum.

The

function of the macrochaetae

and

bristles of the

abdomen

^is doubtless tactile.

They

are capable of

movement

inlife.

In

most

insects the antennae,

and

to a less extent the palpi, are the

main

seat of thetactile sense.

The

cyclorrhaphous Diptera, however,

have

the antennae so modified as to preclude this function. It is

probable that the vibrissa? are functionally tactile,

and

the frontal

and

vertical bristles as well.

The

vibrissa? project straight out ⁱⁿ front near the ends of the ptilinal suture,

and

naturally serve as anterior tactile organs for the protection of the lower portion of the head. Likewise the frontal bristles serve as anterior

and

superior cephalic,

and

the vertical bristles as superior

and

posterior cephalic tactile organs.

The

factthatthe vertical bristlesare almost invaria- bly stronger

and

longer than the frontal bristles strengthens this view.

The

inner vertical bristles correspond in

development

to the vibrissa?.

The

macrochaetae of the thorax, scutellum,

and abdomen

serve as lateral

and

dorsal tactile organs, those of anal

and

preanal

segments

always being the strongest of the

abdomen and

those of scutellum the strongest of the thorax.

The

scutellar are doubtless the

main

dorsal tactile organs,

and

the anal the

main

posterior ones.

The abdominal

macrochaetae,

when

dense

and

of spinose character, pos- sibly serve also as a defense against insectivorous animals, as in

Dcjcania,

Parade

jeania,

Bombyliomyia,

^Hystricia, Hystrichodexia,

and

others.

The

macrochaetae, especially those of the

abdomen,

constitute the

most

recent

form

of specialization inthe

Myodaria, and

are especially characteristic of the Muscoidea.

As

^such,

and

considering further their probable functional character as tactile sense organs, those of the

abdomen

at least can not be expected to furnish valid characters for the separation of higher categories in these flies than species, genera,

and

at

most

tribes.

The

macrochaetae of the head, thorax,

and

scutellum appear to be of far longer standing than those of the

abdomen. With

the excep- tion of

most

of the (Estridae, they are present not only in all

Mus-

coidea,

many

of

which

lack

abdominal

macrochaetae, but also in prac- tically all of the

Myodaria

except the CEstridae already

named and

Conopidae,

which two

families stand well apart

from

the other

Myo-

TAXONOMY

OF

MUSCOIDEAN

FLIES

— TOWNSEND

41