DORSAL VESSEL OF THE IMAGO OF THE BLOW-FLY. 641 
The Anterior Ventricle (Pl. XLV., Fig. 86, v’) is pyriform, 
about r°o mm. in length, with a pair of large obliquely-placed 
ostia ; its broadest part is in front, where its diameter is about 
‘25 mm. Its posterior extremity is narrowed, and communi- 
cates with the third chamber of the heart. 
The third chamber of the heart is fusiform and not more 
than half the diameter of the anterior ventricle. It has a pair 
of obliquely-placed ostia midway between its extremities. 
The two remaining chambers are very long and narrow, 
not more than ‘o6 mm. in breadth, and are more intimately 
connected with the pericardium than the anterior chambers. 
The Valves of the Ostia.—Each lateral opening is protected 
by a pair of semilunar valve flaps, which project forwards 
into the cavity of the ventricle. These valve flaps are partly 
membranous and partly muscular, and their free edges are 
attached by fine fibres to both the dorsal and ventral median 
line in front of the ostia. 
Owing to the small size of the parts in the Blow-fly, it is 
exceedingly difficult to make out the precise disposition of 
the valves, as sections are not favourable to their investigation. 
So far as I can make out they seem to be very similar to those 
described by Graber in the Cockchafer, and by Verloren in the 
larva of Rhyncophora (see p. 638). 
Inter-ventricular Valves.—No inter-ventricular valves exist 
in the dorsal vessel of the imago of the Blow-fly, but there 
are, apparently, a pair of valves opening forwards in the 
aortic bulb, which serve to prevent the regurgitation of the 
blood from the aorta. Neither Verloren nor Graber describe 
any true inter-ventricular valves in the imago stage of the 
insects which they examined. If such valves ever exist they 
must be exceptional. Inter-ventricular valves have, appa- 
rently, only been observed by recent investigators in the larval 
stage. 
The Position of the Ostia has been the subject of much 
difference of opinion. Verloren places them at the junction 
of the several ventricular cavities, and Graber midway between 
these points. My own observations on the Blow-fly agree 
