PLATYHELMIA. 3 1 



in question is simple only one cell thick and columnar, the 

 constituent cells being longer than broad. They are amoeboid 

 and contain large nuclei. 



The food consists of the bile of the host, together with blood 

 and disintegrated liver-substance, resulting from the " rot." This 

 is taken in by the action of the pharynx, which acts somewhat 

 like a piston. By the retractor muscles it is drawn back, when 

 the food rushes into and fills the mouth-cavity. The mouth is 

 now closed and the pharynx brought forwards by the protractor 

 muscle. As, meanwhile, its cavity is enlarged by the contraction 

 of radial fibres in its wall, food passes into it, and (the cavity 

 being diminished by the contraction of other fibres), is then 

 squeezed on into the gullet and intestine. These present a large 

 surface which can at once absorb the fluid part of the food. The 

 amoeboid epithelial cells effect intra-cellular digestion, and perhaps 

 also secrete a digestive fluid which, being poured into the gut, can 

 bring solipl food into solution or a fine state of division. Undigested 

 matter is ejected from the mouth. The digested material diffuses 

 through the intestinal wall to the other parts of the body. 



3. Excretory Organs (Fig. 6, A). Those organs are termed 

 " excretory " (in the narrowest sense), the function of which is 

 to get rid of nitrogenous waste. They here form a network of 

 canals ramifying throughout the body. The smallest of these 

 each terminate in a pear-shaped " flame " cell, containing a large 

 vacuole, and named from the flickering appearance it presents in 

 the living state, and which is probably due to the presence of a 

 row of cilia projecting into the vacuole. The cavities of the 

 flame-cells open into the canals where they terminate, and also, 

 perhaps, into the minute spaces in the tissues, which collectively 

 represent the continuous space, or body-cavity, found around the 

 organs of most animals. The small tubes branch freely, and are 

 united into a network. They open into larger tubes, which, in 

 the anterior quarter of the body, are continuous with four still 

 larger longitudinal trunks, two dorsal (d.b) and two ventral (v.b), 

 and in the posterior three-quarters with a median longitudinal 

 trunk, formed by the union of the four anterior trunks. This main 

 duct (m.d), the largest excretory trunk, runs back, just beneath the 

 dorsal wall of the body, to open by the minute excretory pore (ex.p). 



Histology. The delicate walls of the excretory tubes are made 

 up of a single elastic, structureless layer. They contain a clear 



