SOFT PARTS AND MECHANISM OF THE PROBOSCIS. 391 
which are more especially concerned in the collection and in- 
gestion of food, together with an analysis of what is known of 
its functions and mechanism. 
The soft parts of the proboscis are the muscles, trachez, 
glands, nerve-end organs, and a complex quasi-tendinous 
system of cords contained in the oral portion of the organ. 
These parts may be studied either by dissection or in serial 
sections. 
The greater part of the interior of the proboscis is occupied 
by numerous muscles and large tracheal sacs, which surround 
the fulcrum and tubular mouth. The organ is supplied by two 
pairs of nerves, the small pharyngeal and large maxillary 
nerves. The duct of the lingual salivary glands lies behind 
the fulcrum and terminates in a remarkable valve having 
somewhat the form of a larynx. This is connected by a rigid 
tube with the base of the hollow ligula, through which the 
salivary secretion is discharged into the mouth. 
At the base of the oral sucker, a second accessory pair of 
salivary glands (Pl. VI., sg and Fig. 31, 3) lie one on either 
side of the poculum (p. 144). These are the labial glands, 
the ducts of which discharge their secretion upon the oral 
surface of the terminal sucker. This surface, as has been 
already observed, is channelled by the pseudo-trachee. 
a. The Muscles of the Proboscis. 
The muscles of the proboscis have been very carefully 
and accurately described by Kraepelin [70]. Twelve pairs 
are readily distinguished with two sets of muscle fibres 
near the middle line, which may be regarded either as single 
muscles or as pairs. There are thus fourteen pairs or 
twelve pairs and two azygos muscles, which may be described 
as follows: 
1. Retractors of the Fulerum.—Each of these arises from the side of 
the epistome, runs backwards and upwards, and is inserted into the posterior 
cornu of the fulcrum. In the description of the direction of the muscles, I 
have supposed that the proboscis is hanging down below the head, so that 
the oral lobes are below, and the dorsal or anterior surface of tke organ is 
in front. 
