D. Keilin 
439 
of similar hooks: one towards its anterior margin and with the points directed 
backwards, the other towards its posterior margin and with the points directed 
forwards. Thus each of the intersegmental grooves of the 
abdomen are bordered by two series of hooks with their points 
pointing in opposite directions (Text-fig. 2). This disposition 
of hooks is similar to that in the primary larva of Pollenia rudis 
(Keilin, 1915 a , p. 69) and in both cases it enables the larva 
to fix itself in the tissues of its host. On the ventral surface of 
the eighth or last abdominal segment is the anus which is in 
the form of a cleft surrounded by a perianal protuberance, 
while above and behind this are the only pair of functional 
spiracles which the larva possesses. The spiracles communicate 
with the lateral tracheal trunks through a “felt-chamber" 
which is a short tube filled with a spongy chitinous structure. 
As the anatomy of the larva does not change very much 
during its development, I shall describe it in connection with 
the third stage. I shall confine myself here to a description of 
the mouth-parts as these are the only structures which differ 
considerably in the different stages. 
The Buccopharyngeal armature is composed of the following 
parts (PI. XXIV, fig. 7):—the basal or pharyngeal sclerite 
( b.scl .), which is strongly chitinised, its posterior lateral emargi- 
nation ( l.e .) through which the dilator muscles of the pharynx 
are visible, being very deep and wide. Anteriorly this sclerite 
becomes narrow and lengthens out into a chitinous plate which 
lies vertically in, and protrudes from the mouth, its anterior 
edge being sharpened like the blade of a knife. This anterior 
plate forms the labrum (Lbr.) of the larva. Ventrad to this anterior plate 
is another smaller sclerite, connected with it near its base and close to this 
connection the single salivary duct ( s.d.) 
opens into the floor of the pharynx. The 
sides of this ventral sclerite are strongly 
chitinised and its anterior portion is 
thickened to form the labium ( Ibm .). On 
either side of the mouth is a “lateral 
hook,” a flattened chitinous structure with 
strongly dentate ventral edge (l.h.). 
stage larva of 
Melinda cognata 
Meig. seen from 
the side. 
a 
Fig. 2. Intersegmental portion of the 
first stage larva of Melinda cognata. 
These lateral hooks, hinged upon the sides 
of the ventral sclerite, are moved by ex¬ 
tensor and retractor muscles, the motion of the hooks being in the vertical 
plane of the larva, their function being to scratch or hold on to the tissues of 
the host while the labrum cuts its way forward. 
In the first stage Melinda larva the labrum is ankylosed with the basal 
plate so that the whole of this structure is moved as one piece when the 
