THE HALTERES OF THE BLOW-FLY. 607 
extends into the capitellum, where it encloses a number of fat- 
cells, and multi-nucleated cell-chains, over which the tracheal 
vessel of the scape ramifies in a capillary network. 
The form of the cavity of the scabellum is exceedingly com- 
plex, and it must be regarded as part of the body cavity. 
Rudiments of the Lamina of the Posterior Wing and Small Groups 
of Chordotonal Organs.—The scabellum exhibits several scales 
on its external surface, which are undoubtedly the remains of 
the lamina of a wing. One of these springs from the posterior 
margin of the cupola (Pl. XLII., Fig. 1, sq); this is connected 
by its proximal margin witha second scale (PI. XLII., Fig. 2, sq’). 
These bear a striking resemblance to the squaama and squamula 
of the wing respectively. Beneath the posterior-inferior or 
squamuloid scale there is a small depression—the external 
surface of a group of minute chordotonal organs. It is repre- 
sented in section in Pl. XLIII., Fig. 2, ch. 
A folded remnant of the wing itself projects from the 
posterior border of the scala inferior, and a somewhat hemi- 
spherical swelling is seen at its base (Pl. XLII., Fig. 2, 1); 
this also contains a group of chordotonal organs; it is ap- 
parently the structure described by Bolles Lee [299], and 
may be distinguished as Lee’s organ. 
Lastly, a third and much larger group of similar end organs 
is covered by a projecting hemisphere of thin integument on 
the posterior aspect of the halter (Pl. XLII., Fig. 1, ch). 
There are thus three small groups of very minute chordo- 
tonal organs, covered by thin integument at the base of each 
halter; and three highly-sculptured elevations of the integu- 
ment, containing much larger and more complex organs—the 
two scale and the cupola. 
The Capitellum, or head of the halter, is a subspherical mem- 
branous bulb, divided into two parts by a helicoid septum 
formed of elongated cells. This septum is continuous with 
the septum between the two canals of the scape. 
The capitellum is described by numerous authors as sub- 
spheroidal in form, and it is undoubtedly subspheroidal 
in the living insect; but after death, and especially when 
40 
