8 + THOMPSON YATES LABORATORIES REPORT 
The muscle attached to the labrum on each side consists of two bundles of 
fibres lying side by side, having an extensive origin from almost the whole of the 
upper median surface of the clypeus from before backwards. Their fibres are 
directed backwards and collect together in a fan-like manner, to be inserted into the 
projecting chitinous base of the labrum (plate XVIII, fig. i and XVII, fig. i Ibr.m.). 
The muscles in connection with the base of the epipharynx are two lateral 
groups arising from the lateral outer wall and free edges of the fulcrum ; a few fibres 
probably arising from the adjacent inner wall of the clypeus. The fibres project 
vertically downwards, and are inserted into the horizontal plate of chitin on either 
side of the epipharynx (plate XVI, fig. 2 e.m.) 
The third set of muscles arise from the upper inner surface of the clypeus on 
each side of the labral muscle mass ; the fibres run backwards and downwards to be 
inserted into the upper chitinous plate of the ascending portion of the pharynx — each 
muscle being divided into a central and two lateral portions, inserted into the central 
membranous and anterior and posterior chitinous portions of the wall respectively 
(plate XVIII, fig. 1, and XVII, fig. 1 p.m.). The remainder of the clypens is occupied 
by tracheae and nerves for supply of the above muscles, and it is lined by loose 
spongy fatty connective tissue. 
The pharynx is that part of the alimentary tract, lined with chitin, which 
extends from the base of the proboscis to the commencement of the oesophagus at 
the junction of the head and neck. It consists of two portions, a short anterior 
ascending and a longer horizontal portion, the latter passing through the ganglionic 
ring formed by the supra- and infra-oesophageal ganglia and their commissures. 
Here it forms a large chamber — the pumping organ. Dim mock 1 describes this part 
of the pharynx as the oesophagus. The first part of the pharynx is narrow and is 
a tubular continuation of the epipharynx above and the hypopharynx below ; it 
passes upwards and backwards, ending opposite the furrow separating the clypeus 
from the head. Here the pharynx suddenly turns backwards and is continued on as 
the second part of the pharynx. The first part of the pharynx consists of two plates 
of chitin, an upper and a lower ; the former limits the clypeus internally ; it is not 
completely chitinous, in fact only its anterior and posterior portions are chitinised and 
thin off towards the centre of the plate which consists of a membrane covered with 
flattened epithelial cells (plate XVIII, fig. 1, and XVII) ; to this membrane are 
attached the oblique central fibres of the pharyngeal muscle. On the pharyngeal 
surface of the anterior chitinous portion of this upper wall of the pharynx are a few 
low conical papillae (taste papillae) (plate XVIII, fig. 1). The posterior upper edge 
of this wall is curved slightly outwards upon itself and is attached to the upper wall 
of the second part of the pharynx by a folded band of chitin. 
The ventral wall of this part of the pharynx is a stout plate of chitin, anteriorly 
continuous with the hypopharynx, posteriorly with the ventral wall of the second 
1. Dimmock, The Anatomy of the Mouth parts, etc. Boston, 1881. P. 13. 
