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, tracheae, 

 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 (PI. VI., sg and Fig. 31, j) 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-tracheae. 



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 Fulcrum. 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 the organ is 

 in front. 



