in PLATODES ORGANS OF ADHESION 145 



numerous pairs of lateral intestinal branches succeed each other more 

 or less regularly, they are separated by equally regular muscle septa 

 or dissepiments. This is the case in elongated Polydada and Triclada, 

 and especially in the marine Triclada (Gwnda), in which the lateral 

 intestinal diverticula are unbranched. In all cases, when sexual maturity 

 is attained, the formation of septa is more or less obliterated by the 

 development of male and female germ glands, which are generally 

 placed between the intestinal branches. 



VII. Organs of Adhesion. 



These are very widely spread among the Platodes. One division 

 of the Polydada, that of the Cotylea, is characterised by the possession 

 of a muscular sucker, which lies about the middle of the ventral 

 surface, always behind the mouth and the genital apertures. By 

 means of this sucker the Cotylea often temporarily attach themselves 

 to some object on the sea bottom. Besides this, very many 

 Turbellaria of the most various divisions, possess special adhesive 

 cells with rough surfaces which serve for attachment. 



In the parasitic Trematoda and Cestoda the organs for adhesion are 

 specially strong and variously developed. They here serve to fasten 

 the body either outwardly to the skin, or inwardly to the intestinal 

 wall of the animal inhabited, or host. They are principally pit- and 

 disc-like suckers, with or without stalks, whose number, form, and 

 arrangement are of the greatest importance in classification. We 

 select only the most important. 



In the digenetie Trematoda there are at. the most 2 pit -like 

 suckers (Fig. 106), one of which, in whose base the mouth nearly 

 always lies, is found at the front end of the body as oral sucker (ms). 

 The other is either wanting (Monostoma), or lies at a variable distance 

 from the anterior end on the ventral side (bs) (Distoma), or at the 

 posterior end of the body (Amphistoma). 



In the monogenetie Trematoda there are often 2 suckers or 

 sucker-pits on each side of the mouth. Besides these, at the posterior 

 end of the body, there is a very large stalked ventral sucker (Tristoma) ; 

 or the hinder portion of the body becomes transformed into a large 

 sucker-disc, which again may carry sucker-pits in varying numbers and 

 in symmetrical or asymmetrical arrangements (Polystoma). 



In the class of the Cestoda also the presence of suckers or sucker- 

 pits is the rule (Fig. 117, p. 164). They here always lie at the 

 foremost end of the body, singly (Amphilina), two in number (BotTirio- 

 cephalus, Schistocephalus, Tricenophorus), or four in number (Tceniadce, 

 Tetrarhynchidce, Tetraphyllidce). In the Tetraphyllidce they often have 

 long stalks. 



As a further strengthening of the apparatus for adhesion there are 

 often hooks, ridges, teeth, etc., as in the ventral suckers or on the 

 adhesive discs of many monogenetie Trematoda, in the suckers of many 

 VOL. i L 



