THE HALTERES OF THE BLOW-FLY. 613 



supporting the chordotonal thread is probably developed from 

 the cell protoplasm. 



Lee's Chordotonal Organ. Lee correctly describes a remark- 

 able organ situated on the under and posterior part of the 

 scabellum (PI. XLIL, Fig. 2, /). This organ consists of a thin 

 dome of integument containing a sensory ganglion surmounted 

 by a number of minute sensory rods, 3 JJL to 4 ^ in diameter, or 

 even less, containing exceedingly minute chordotonal threads. 

 Lee [299, p. 368] says : ' The nerve to the halter divides 

 as soon as it enters the base into four principal branches ; one 

 enters a ganglion (bouquet} of great fusiform cells, and sup- 

 plies the organs of the basal plate ; two others pass in the 

 halter beyond this ganglion, and, diverging from each other, 

 enter ganglia similar to that of the basal organ and terminate 

 in the scapal organs ; whilst a fourth and smaller branch quits 

 the principal trunk on a level with that to the basal ganglion, 

 passes to the opposite side of the halter, and enters a ganglion 

 formed at its proximal end of great fusiform cells with large 

 nuclei ; beyond these there is a mass of minute nuclei, and then 

 a layer of minute highly refractive bodies in the form of stylets, 

 and a second layer of minute nuclei immediately below the 

 hypodermis. Transverse sections show the structure of this 

 organ better, which in these appears as a perfectly normal 

 chordotonal organ, one may say a typical one. The fusiform 

 cells are the ganglion cells, the proximal mass of small nuclei 

 represent the basal nuclei, the typical chordotonal elements, 

 stylets or forks are the scolopifera (Nervenstifte, scolopale 

 Korperchcn], and the small distal nuclei the distal nuclei of 

 Graber. In all these points the organ differs in no respect from 

 chordotonal organs in general. The stylets only demand 

 special consideration.' 



' It is well known that Leydig [269] described two kinds of 

 stylets in the nerve terminations of the halteres a slender 

 form with acuminate capitella, and a thick form with rounded 

 heads ; these two forms are not found intermixed, but arranged 

 in two bundles so that the slender stylets, about a dozen, 

 form a group well separated from the far more numerous 



