1935 ] 
Immature Stages of Macrocera anglica 
29 
eral ends of the frame articulate with two well developed 
arms (c.r.) which pass ventral to the labrum. Each arm is 
provided with a fan-shaped organ, composed of several 
curved teeth, whose forward and backward movements help 
to direct the food particles towards the mouth opening. The 
labrum is a fleshy hood-like protuberance extending forward 
and downwards to recurve within the mouth. It is provided 
with 8 pairs of dorsal papillse. 
The mandible (Fig. 5) is elongated and consists of a con- 
vex dorsal and a large flat ventral lamella. The dorsal la- 
mella is provided with one tooth and a well developed pro- 
stheca at the inner basal angle. On the medial border, the 
mandible carries three teeth and a small rounded tubercle. 
The muscles operating the mandible are well developed 
and consist of an abductor and an adductor muscle. The 
abductor muscle (ab. m. Fig. 5) takes it origin from the 
posterior and lateral side of the epicranial plate and consists 
of five bundles which converge towards the upper slender 
tendon which is inserted to the upper angle of the mandible. 
The adductor muscle (ad.m) arises partly from the lateral 
and partly from the ventral surface of the epicranial plate. 
The ventral and dorsal bundles converge towards the adduc- 
tor tendon to be inserted at the inner basal angle of the man- 
dible ventral to the prostheca. 
The maxillse lie ventral and parallel to the mandibles. 
Each maxilla (fig. 6) consists of two lobes. The inner lobe 
or maxilla proper is cultriform and carries seven teeth, the 
last of which is strongly chitinised and more rounded than 
the rest. The outer lobe is provided with an oval area an- 
teriorly, which is covered with a transparent membrane and 
bears one large circular and five small sensory papillse. The 
maxilla is produced posteriorly as a strongly chitinised rod 
which serves for the attachment of the adductor muscle. The 
two maxillse are supported along their posterior border by 
two triangular plates — the maxillary plates (mx. pi. Fig. 3) 
— which meet along the mid-ventral line. 
The maxilla is provided with an adductor and an abduc- 
tor muscle. The first consists of several bundles which arise 
from the apex and lateral margin of the occipital foramen 
and are inserted to the rod-shaped process of the maxilla. 
