TREMATODA 



Ut. 



Oat. 



tr c.v. 



the parenchyma in a dorso-ventral direction ; their diverging brush- 

 like ends are inserted on the inner surface of the cuticle (fig. 67). 



The suctorial discs seem to 

 be specially differentiated parts 

 of the musculo - dermal tube. 

 Their concave inner surface is 

 lined by the continuation of the 

 cuticle and their vaulted ex- 

 ternal surface is covered by a 

 more dense tissue that frequently 

 takes the form of a shiny mem- 

 brane. 



The principal mass of the 

 suctorial discs consists of mus- 

 cular fibres which run in three 

 directions equatorial, meridi- 

 onal and radial. The equa- 

 torial fibres correspond to the 

 annular muscles, the meridional 

 fibres to the longitudinal mus- v de 

 cles, and the radial fibres to the 

 muscles of the parenchyma ; the 

 radial fibres are always most 

 strongly developed. The func- 

 tion of these muscles is con- 

 sistent with their position ; the 



meridional fibres flatten the 



suctorial disc and diminish the 



depth of its cavity, so that the 



internal surface may touch the 



object to be held ; if the equa- h. 



torial fibres then contract, the FIG. 66. Polystomum integerrimum 



i , f from the urinary bladder of the frog. 



suctorial pore rises by means of (After Zellen) ^ intestine; h., large 



longitudinal stretching, and the hook of the sucker ' hk -> sm aiier hook- 



, . lets ; Lc.v., longitudinal canals of the 



inner Slirlace Ol the organ IS vitelline sac; o., oral orifice ; oot., ootype ; 



drawn in by the contraction of - ovar y ; S -P- suctorial P ore s <>* the 



J disc ; tr.c.v., transverse canals of the vi- 



the radial muscles. Thus the telline sac /., uterus with ova ; v., en- 



sucking disc becomes adherent. ^du^S; tatMLFSTE 



Usually also there is a Sphincter telline sac and testicular vesicles are not 



at the border of the suckers, seen ' ( Ma g nified -> 



which plays its part during the act of adhesion by constricting 



in a circular manner that part of the mucous membrane to which 



s.p 



