THE WING ORGANS. 621 
is united with the marginal nervure by a small transverse 
branch; each pore exhibits a dark brown margin, enclosing 
a small circular opening, around the margin of which there is 
a clear space surrounded by an outline which exhibits a double 
contour. ; 
‘This collection of pores is prolonged in either direction in 
a single line of similar pores. After clearing the wing with 
potash and compressing it, a very distinct view of its interior 
was obtained. A thick tracheal stem is observed. After 
describing the position of the vessel, he continues: ‘ Closely 
related to this tracheal tube there is a nerve of moderate size 
which gives off a series of branches to the pores, resembling 
the nerves to the crista of the Locustide in their arrangement. 
These branches terminate in end organs, which are related 
to vesicles beneath the integument. The vesicles are some- 
what elongated, and lie almost at right angles to the end 
organs. 
‘The vesicles are the clear spaces surrounded by a double 
contour already mentioned. Each vesicle lies undera cuticular 
pore—the transparent spot surrounded by a dark margin in 
surface views. 
‘The nerve terminals consist of a nucleated enlargement, 
which is to be regarded as a ganglion-cell followed by a second 
fusiform enlargement, in one of which there is a thread-like 
structure ; this is not, however, very distinct.’ 
Graber concludes that if his observations are correct, this 
is a chordotonal thread, and adds: ‘Opposite to the place 
where the vesicle is related to the cuticular pore, several 
diverging bands spring from a single point, and are inserted 
into the integument (Fig. 81, A, a), giving them the character 
of chordotonal organs.’ 
From Graber’s drawing and my own observations on the 
Blow-fly, I think it indubitable that the bright spot which he 
regards as a pore is really due to the presence of a corpuscle 
beneath the integument similar to that which I have figured 
from the great chordotonal organs of the halteres. In the 
Blow-fly the wing organs are situated on the remigium, or base 
