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 g, g 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. 
Fic, 79.—A semi-diagrammatic representation of three of the nerve end organs of 
the cupola of the halter of a Blow-fly. ch, capitellum of the chordotonal thread ; 
ch’, the chordotonal thread ; g, ganglion cell ; 7, nerve-fibres ; s, 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 
developed 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 
