440 
Melinda cognata Meigen 
labrum is being used as a cutting instrument. In Pollenia rudis on the other 
hand, the labrum is articulated with the basal plate and thus moves inde¬ 
pendently (PL XXIV, fig. 12). 
(c) Second stage larva (Text-fig. 3). 
The average length of the second stage larva is 7 mm. During this stage 
the larva is more opaque than in the first stage but its internal organs are still 
visible by transmitted light. The three thoracic segments, 
near the anterior border, show a few series of hooks with 
backwardly directed points, while each of the first five ab¬ 
dominal segments bears two series of hooks as in the previous 
stage. The three last segments show only the posterior series 
of hooks. The larva has now become amphipneustic, and the 
anterior prothoracic spiracles usually bear four to six short 
papillae (PL XXV, figs. 15, 17 and 25). 
In some cases there are four or five of these papillae on 
the one spiracle and five or six on the other. I described a 
similar case in the larva of Muscina assimilis Fall. (1917, 
p. 410). 
The structure of the postabdominal spiracles is the same 
as in almost all the Cyclorhaphous larvae (PI. XXV, figs. 23 
and 24). There are two spiracular tubercles and each pos¬ 
sesses two oval clefts surrounded by a peritreme ( / per.) of 
irregular form. Near the outer border of this peritreme is a 
small white spot which marks the external opening of the 
perispiracular glands (o.) and this opening is surrounded by 
a series of chitinous hairs expanding in the form of a fan. Each spiracular 
tubercle, near its internal border, shows a scar (sc.) which represents the open¬ 
ing through which the tracheae of the previous larval stage were expelled. 
Occasionally an abnormal spiracle is found in which one of the peritremes 
is double so that the tubercle has the appearance normal to the third stage 
larva (PL XXV, fig. 24, cf. also a similar abnormality in the third stage, p. 441 
and PL XXV, fig. 21). 
The Buccopharyngeal armature (PL XXIV, fig. 10) has now the appearance 
which is very usual in Cyclorhaphous larvae. The above mentioned figure 
shows clearly its structure and the relations of the different parts to one 
another. The basal sclerite is large and the floor of the pharynx, as in all 
parasitic Dipterous larvae, is without the longitudinal ridges which are so 
well developed in saprophagous larvae (cf. Keilin, 1915 a, pp. 127-142). 
Fig. 3. Second 
stage larva, of il/e- 
linda cognata seen 
from the side. 
(d) Third stage larva. 
The full-grown larva, when ready to pupate, is 12 mm. long and 0-6 mm. in 
diameter; the boundaries between the segments are not clearly marked and 
