DORSAL VESSEL OF THE IMAGO OF THE BLOW-FLY. 639 
2. THE DORSAL VESSEL OF THE IMAGO OF THE 
BLOW-FLY. 
The dorsal vessel commences near the posterior border of 
the fifth abdominal segment, arches forward immediately 
beneath the integument, and terminates in the aorta at the 
inferior margin of the mesophragma. 
It can be most readily seen im situ by making a vertical 
longitudinal section, a little on one side of the median line, 
Fic. 86.—A section through the dorsal part of the abdomen of a Blow-fly, showing 
the dorsal vessel. @, aorta; ch, chyle stomach ; 7, intestine ; », mesophragma ; 
Pp; pericardial septum ; sc, scutellum; v', v”, v''’, 2nd, 3rd, and 4th ventricular 
enlargements of the dorsal vessel. The longitudinal fan-like alar muscle is seen 
covering the two anterior enlargements, 
through the body of a Blow-fly which has been previously 
hardened in a I per cent. solution of potassium bichromate, 
and afterwards in strong alcohol (Fig. 86). 
The anterior part of the dorsal vessel is then seen between 
the intestine and the abdominal wall; the posterior part is 
more difficult to trace, and can only be studied in serial 
sections and when the whole pericardium and dorsal vessel have 
been removed from the body of an insect. 
This can be done by taking away all the structures which 
lie beneath it, so as to leave the pericardium on the inner 
surface of the dorsal wall of the abdomen. The posterior 
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