PARORCHIS ACANTHUS, A NEW TREMATODE. 347 



has a few spines near the ventral sucker, but the dorsal 

 surface has none. 



The usual length of adult individuals is 3 — 5 mm. Sexual 

 maturity is seldom attained below a length of 3 mm. The 

 various measurements which will follow have reference to an 

 individual of about 4 mm. length. The breadth of the head is 

 fairly constant, '82 — '87 mm. In the extended state the 

 breadth of the rest of the body is 1*2 — 1*4 mm., but on 

 contraction the posterior acetabular region may be as much 

 as 3 mm. broad. The average breadth is about one third 

 of the length of the body. In young examples the cephalic 

 breadth is proportionately greater than in adults. The 

 thickness of the body varies from "4 mm. in the neck to 

 •8 mm. at the ventral sucker. The post-acetabular region 

 has an average thickness of '5 mm. 



The suckers are globular in shape and extremely muscular. 

 The apertures are circular. The oral sucker may attain a 

 diameter of '5 mm., while the ventral sucker is usually rather 

 more than twice as great. In young specimens the proportion 

 between the diameters of the two suckers more nearly approxi- 

 mates 2 : 3, the oral sucker being proportionately larger. 



The cuticle is well developed and has an average thickness 

 of "005 — "007 mm., although in contracted parts it may be 

 twice as thick. The spines, where they occur, are imbedded 

 deeply in it. The anterior spines have a length of "019 mm. 

 Passing backwards they increase in size, and may be found 

 as long as "031 mm. with a base measurement of •012 mm. 



The alimentary system is very well developed. There is a 

 short thin-walled pre-pharynx, '11 mm. long (Plate 21, fig. 2, 

 p.ph.). The pharynx is muscular, and measures '24 by '17 mm. 

 On contraction of the animal the pharynx is thrust up inside 

 the pre-pharynx, and the walls of the latter instead of con- 

 tracting are bent down round the pharynx. The oesophagus 

 is about three times as long as the pharynx. Its walls are 

 crinkled so that numerous small dilatations are formed. In 

 section its dorso-ventral diameter is much greater than its 

 transverse diameter. The epithelium of its lumen is well 



