612 



THE SENSES AND SENSORY ORGANS. 



These show that the vesicles seen in surface sections surround 

 true chordotonal organs : the bright highly-refractive central 

 dot is the capitellum of a chordotonal thread. Fig. 79 is 

 a semi-diagrammatic representation of the relations of the 

 vesicle and chordotonal rod. I have been unable to make 

 out the exact manner in which the nerve-cells #, # are con- 

 nected with the chordotonal threads, but as the latter are 

 distinctly fixed at either end, and the nerve-cells certainly 

 communicate with the vesicles, I think it indubitable that the 

 connection is similar to that of other chordotonal organs, and 

 is correctly represented in the central organ in the figure. 



I , ; . 79. A semi-diagrammatic representation of three of the nerve end organs of 

 the cupola of the halter of a lilow-fly. f/i, capitellum of the chordotonal thread ; 

 fA\ the chordotonal thread ; g, ganglion cell ; , nerve-fibres ; j, seta on the 

 surface between the so-called papilla: ; sac, sac containing the suspended capitel- 

 lum of the chordotonal thread. 



These organs are similar to those of the wing nervures of many 

 insects (p. 620) and of the pygidia of Notochrysa (p. 629). 



I think there can be no doubt the chordotonal thread is 

 k-voloped in relation with the nucleus, perhaps from the 

 nucleus itself of the cell which contains it, as in some of my 

 preparations stained with picro-carmine the head of the 

 chordotonal thread is intensely stained. The vesicle which 

 contains it is in this case a large vacuole, and the tissue 



