502 A XKW A\ IAN THK.MATUDE, 



does occur in some yeuera, e.g., Ooryuderu, but here the couclusiou is I'ureed upon 

 me that the pharynx is present, and that no distinct oral sucker is represented. 

 The posterior sucker, (1.133 mm. long-. 0.095 mm. broad, with thickness of wall. 

 0.038 mni., opens into the narrow cavity between the doisal body wall and the 

 median process of the clinging plug. 



The Clinging Plug. — The clinging jjlug comprises (1) a main ovoid mass, 

 larger basally, divided into two lateral lobes by an oblique septum running from 

 the dorsal body wall at half its length anteriorly to the ventral wall at its hinder 

 level posteriorly. In this septum lun the two branches of the alimentary canal 

 and certain large excretory spaces (PI. xsvi., fig. 4, int. ex.). Anteriorly the 

 mass projects forward as two smaller lateral lobes, which end a little forward of 

 the narrowest diameter of the cup (PI. sxvi., tig. 3, d. ic.) : (.2) a median process 

 attached to the dorsal body wall anterior to the main lobes, narrowing distally, 

 and enlarging into two small flattened lobes, capable of being bent over towards 

 the ventral wall (PI. xx\"i.. tig. 3, m.d.p.), but, when extended, reaching to the 

 boi-der of the cup; (3) a lamellar fold arising from the ventral body wall at the 

 anterior level of the main mass, and expanding on both sides to form a collar 

 embracing the median jjrocess, and the doi'sal and ventral processes next men^ 

 tioned (PI. xxvi., fig. 3, r.ic.) ; (4) a capitate process arising from the base of the 

 median lobe dorsally and extending forwards to the level' of the cup margin (PI. 

 xxvi., fig. 3, pr2) ; and (5) a similar larger ventral process arising at the base of 

 the lamellar fold, and projecting forwards to the same distance (PI. xxvi., fig. 3. 

 pn). 



The main ovoid mass of the plug arises from the dorsal Ijody wall pos- 

 terior to the narrowest regri<m of the cup (PI. xxvi., fig. 3) . It is divided into two 

 lateral lobes, into which muscle fibres pass through the base of attachment from 

 l)<)tli an anterior and posterior direction. Vitelline glands are found throughout 

 this division of the i)lug. but do not occur in any of the other pi'ocesses. 



The large gland spoken of by Brandes (1891, p. 3t)0l as secreting a corrod- 

 ing substance, is situated just behind the base of attachment of this main doi'sal 

 mass (Pi. xxvi., fig. 2, gl.). The aiTangement of the follicles of the gland point 

 to the fact that the secretion is carried fonvard by a number of fine ducts, but 

 no connection can be traced between this gland ^ind certain ducts containing a 

 definite secretion, whicli appear at the posterior extremity of the main mass of 

 the plug, and run forward in the accessory processes. 



The cup in which the plug lies occupies almost one third of the total body 

 length, and is divided posteriorly into two lateral cavities by the obliiiue sei)tum 

 before mentioned (PI. xxvi., fig. 4, c.c). 



Miiscidature. — Lying directly below the cuticle are two layers of nuisde 

 fibres, an outer circular, and an iiuier longitudinal layer. In addition, definite 

 strands of oblique nuisde extend tl.rouuh tlie parencliyma from tlie outer to t\n- 

 inner wall of the cup. 



The region of the ventral sucker is very nuiscular. and it is liere that thi- 

 two main dorsal longitudinal bamls of nuisde have their origin. These band> 

 run back below tlie dorsal surface to tlie i«)sterior end of the body, and adil 

 greatly to tiie efifectiveness of the ])liig as explained l)y lirandes (1891, ji. 5591. 

 Contraction of these fibres causes a sharpening of the angle between the anterior 

 and posterior i-egions. and tlie pressure of the individnal jiarts of the iiiui; ai;ain>t 

 one another. 



