THE SENSES AND SENSOR Y 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 ri 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 o - 2S 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 n), 

 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 



INSCRIPTION OK PLATE XLII. 



The hnltcres of the Blow-fly and of Eristalis : 



].- I( ;. i. The right halter of a Blow-fly seen from above. <-, the cupola ; ch, 

 chnnlotonal membrane ; sc, scala superior; sq, squamoid scale ; /, ovoid eleva- 

 tion at the base of the halter. 



IK; 2. The left halter seen from below. /, Lee's chordotonal organ; sc', scala 

 inferior ; s<j', the squamuloid scale. 



I to. 3. A semi-diagrammatic representation of the right halter of Eristalis tenax seen 

 from below and behind, s, the septum of the capitellum ; sf, scala\ The arrows 

 K IIK smt the direction of the movement of the fluid in the canals towards the 

 seal.'-. 



IMC. 4. A surface view of a part of two of the ridges of the cupola of a Blow-fly seen 

 with a ,' oil immersion objective. 



IMC. 5. A surface view of a part of one of the transverse arcades of the scala of a 

 r.lnw-lly, seen with a -fa oil immersion objective. 



IMC. (>. A surface view of the chordotonal membrane (c/i, Fig. i), seen with a } inch 

 objective. 



FlG. 7. A surface view of two of the oval bodies of the same seen with a ^ oil im- 

 mersion. These are apparently groups of chordotonal threads. 



