604 THE SENSES AND SENSORY ORGANS. 
their great complexity is overlooked. That they are highly 
modified wings is true, but that they are rudimentary organs 
is in no sense true. 
The halteres obtain their greatest complexity in the Muscidae, 
and are apparently more highly developed in Calliphora than 
in the great majority of the Diptera ; indeed, I know no insect 
in which the special structures at their base are so highly 
developed. 
General Description—The superficial resemblance of the 
halteres to drumsticks is well known, but the proximal extre- 
mity (Pl. XLII.) forms a dilated subpyramidal organ, which 
may be termed the scabellum. This, with the stalk, or scape, 
and the head or capitellum must be included under the term 
halter. 
The halter of the Blow-fly varies from 1°r mm. to 1'4 mm. 
in length, the scabellum is 0°31 mm., the scape is 0°51 mm. in 
length, and the head is from 0:28 mm. to 0°34 mm. in diameter. 
The scabellum articulates by a freely movable joint with the 
crutch-like crura of the metapleuron (PI. VIII., Figs. 10 and rz), 
and is moved by four muscles, which are attached to minute 
processes arising from the proximal border of the scabellum. 
Movements.—The halter moves with the wings, but apparently 
DESCRIPTION OF PLATE XLII. 
The halteres of the Blow-fly and of Eristalis : 
Fic. 1.—The right halter of a Blow-fly seen from above. c, the cupola; ch, 
chordotonal membrane ; sc, scala superior ; sy, squamoid scale ; ¢, ovoid eleva- 
tion at the base of the halter. 
Fic 2.—The left halter seen from below. /, Lee’s chordotonal organ; sc’, scala 
inferior ; sg’, the squamuloid scale. 
Fic. 3.—A semi-diagrammatic representation of the right halter of Eristalis tenax seen 
from below and behind. 5, the septum of the capitellum ; sc, scale. The arrows 
represent the direction of the movement of the fluid in the canals towards the 
scala. 
Fic. 4.—A surface view of a part of two of the ridges of the cupola of a Blow-fly seen 
with a 'y oil immersion objective. 
Fic. 5.—A surface view of a part of one of the transverse arcades of the scala of a 
Blow-fly, seen with a yy oil immersion objective. 
Fic. 6.—A surface view of the chordotonal membrane (ch, Fig. 1), seen with a } inch 
objective. 
Fic. 7.—A surface view of two of the oval bodies of the same seen with a 41, oil im- 
mersion. These are apparently groups of chordotonal threads. 
