114 J. C. W. Kerrsuaw, 
The maxillae and mandibles are always described as being 
withdrawn into the head-capsule, but according to the above 
description their position of attachment is nearly normal. The 
apposition of the maxillary plates against the lateral edges of the 
elypeus has forced the mandibles slightly within, but this is the 
only withdrawal of these organs into the head-capsule. 
To illustrate this view of the position of the mouth-organs, 
which was first brought to my notice by Mr. F. Muık, and demon- 
strated by him in this particular insect, we can consider a eircular 
oral margin with the trophi in the normal position, consisting of 
labrum, elongated mandible and maxillae with elongated palpifers, 
as is found in certain Diptera. If in such a mouth the maxillae 
and labrum were to become triangular and their edges met from 
base to tip, then the mandibles and palpifers would become internal 
and the mouth become beak-like, similar to the Homopterous mouth. 
The labium (Zab) forms a long six-jointed proboscis having a 
deep trough along the dorsal surface, into which pass the setae 
after leaving the “beak”. The ventra! portion of the first segment 
is produced into a chitinous process (Fig. 65p), the tip of which is 
bent upwards and forms the attachment of the protractor muscle 
of the proboseis, the other end attaching to the framework of the 
salivary syringe. Near the foot of the basal process arises a pair 
of retractor muscles attached at the other end to the maxillary 
bridge (Fig. 6 Mb). By the aid of these opposing muscles the 
proboseis can be thrust out or drawn into its membraneous base. 
The tip of the labrum (ZÖb) fits into the dorsal groove and forms a 
guide for the proboseis. 
The oesophagus (Oe) is a slender, delicate tube, slightly swollen 
and bent at riecht angles behind the oesophageal nerve-ring. 
Anteriorly the walls are flattened horizontally. the lateral margins 
being turned slightly upwards; the walls become chitinized, especially 
the ventral one, which is attached anteriorly to the elypeus by a 
strong chitinous process. This forms the pharynx (P). Powerful 
muscles (Fig. 6 Pm) connect the dorsal plate with the clypeus, 
whose contraction draws the dorsal from the ventral wall, and on 
relaxing allows the plate to resume its former position by its own 
elasticity. The alternate contractions and relaxations induce a 
f 
have called the maxillary plate must be looked upon as a development of 
the gena. 
