THE BLUE-BOTTLE FLY. 91 
hairs, between which are pellucid dots. These are 
small sacculi, opening by pores on the surface, like 
those of the maxillary palpi.* The eyes. Cut off a 
portion of one of the eyes and spread it out. Notice 
the hexagonal facets of the horny integument. The 
halteres. Cut one out with part of the thoracic in- 
tegument attached. It is composed of three portions 
—hbase, pedicle, and globe. Notice the large vesicles 
in the globe, and the bright spots on the base. The 
legs. Made up of the fellowing pieces—coxa, troch- 
anter, femur, tibia, and tarsus. The last is five- 
jointed, the last of which bears a pair of pads and a 
pair of claws above them. The spiracles are two on 
each side in the thorax, and in the abdomen the male 
has eight and the female six on each side. Trace 
down the tracheze to one of the abdominal spiracles, 
and cut the integument all round it. Examine with 
the inch objective. 
12. The wings.—Cut off one of the wings close to the 
thorax, and examine it. The outer marginal vein is 
called the costa, or costal ven. From the thorax 
proceed two large trunks, each of which splits up 
into several longitudinal veins, and these two sets of 
longitudinal veins are connected by a short transverse 
vein. Of the upper set of longitudinal veins, the 
lowest, which is met by the transverse vein, is the 
cubital vein ; the next above is the radial vein; the 
next, the swb-costal vein ; and the next, the medvas- 
tinal vein, Of the lower set, the upper vein, which 
is met by the transverse vein, is the discotdal vein ; 
near the margin of the wing it is bent up so as nearly 
* These are better seen in a fly that has been boiled for a short time 
in a solution of potash, well washed, and kept twenty-four hours in gly- 
cerine, The organs should be examined in a drop of glycerine, on a glass slide, 
