16 W. BALDWIN SPENCER. 



upper lip; (2) the pharynx; (3) the oesophagus; (4) the stomach ; 

 (5) the rectum. Of these parts the first three are equivalent 

 to the fore-gut, the fourth to the mid-gut, and the fifth to 

 the hind-gut of other Arthropoda. 



(1) The Mouth and Oral Papilla or Upper Lip. — 

 This lies in the mid-ventral line (figs. 1, 2, 5), and in both 

 males and females is prominent. The outline of the papilla is 

 triangular, with the angles broadly rounded ofi" and the apex 

 pointing anteriorly. It is sunken in a pit, the sides of which 

 closely embrace it, producing thus the appearance of a groove, 

 which on the posterior side of the papilla is slightly enlarged, 

 indicating the actual mouth opening. A median longitudinal 

 section (fig. 33) shows the relationship well, the groove being 

 cut through anteriorly, and the mouth opening and pharynx 

 posteriorly. The cuticle of the external surface of the body 

 dips down into the groove and covers the surface of the 

 papilla, being especially thick (fig. 32, Gr.) when, at the 

 deepest part of the groove, it turns downwards to spread over 

 the papilla. This part serves as an attachment for muscles 

 concerned with the papilla and pharynx. 



Hoyle^ has described two and possibly three sets of muscles 

 in the papilla of P. protelis; whilst Stiles^ and Lohrmann 

 agree in describing, in the forms examined by them, only a 

 single set, viz. those running parallel to the length of the 

 body. In P. teretiusculum only the latter are present, and 

 they spread out into a fan-shaped mass, which runs forwards, 

 the fibres converging to be inserted anteriorly into the thick- 

 ened cuticle at the innermost end of the groove surrounding 

 the papilla (fig. 32, 3/5), From the bottom of the groove on 

 each side of the papilla anteriorly there is a plate-like project- 

 ing of cuticle passing upwards into the body-cavity. To the 

 inner sides of these two plates muscles converge, which run 

 downwards and forwards (fig. 32, M 6) from the front and side 

 walls of the pharynx. 



From the firm attachment afi'orded by the thickened cuticle 



' Loc. cit., p. 175. 



3 Loc. cit., p. 121. 



