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 (Pi. XLIL, Fig. i, sq) ; this is connected 

 by its proximal margin with a second scale (PI. XLIL, Fig. 2, sq'). 

 These bear a striking resemblance to the squama 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 PI. XLIIL, 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 XLIL, Fig. 2, /) ; 

 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 (PI. XLIL, Fig. i, 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 scalse 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 



