230 



MANUAL OF ZOOLOGY. 



DIVISION I. PLATYELMIA. This section includes those Scole- 

 cida which possess a more or less flattened body, usually some- 

 what ovate in shape, and not exhibiting anything like distinct 

 segmentation. The division includes two parasitic orders 

 the Tceniada and the Trematoda, and one non-parasitic order 

 viz., the Turbellaria. A sub-order, however, of this last, the 

 Nemertidce, does not conform to the above definition ; but their 

 other characters are such as to forbid their separation. 



ORDER I. TCENIADA (Cestoidea). This order comprises the 

 internal parasites, called Tape-worms (Cestoid worms), and 

 the old order of the "Cystic Worms" (Cystica) ; the latter 

 being now known to be merely immature forms of the Tape- 

 worms. 



The Tceniada are Scolecids in which the body of the adult 

 is elongated and composed of flattened joints, the anterior ex- 

 tremity ("head") armed with hooklets, or suckers, or both 

 combined. There is no mouth or alimentary canal, and the 

 young pass through a metamorphosis. The mature animal is 

 hermaphrodite. 



In their mature condition, the Tceniada (see figs. 113 and 

 114) are always found inhabiting the alimentary canal of some 



Fig. 113. Morphology of Tceniada. a Head and a few following segments of Tcenia 

 mediocanellata ; b A few segments of the same further removed from the head ; 

 c and d Segments progressively further removed from the head, all of the natural 

 size ; e Head of the same, enlarged ; ft A single proglottis of the same, with its 

 branched ovary and lateral genital pore, enlarged two diameters ; f Embryo of Teenia 

 bacillaris, with six booklets ; g Cysticercus cellulose, with its booklets and suckers, 

 its wrinkled neck, and its caudal vesicle, enlarged. (After Leuckart, Van Beneden, 

 and Weinland.) 



warm-blooded vertebrate animal; and they are distinguished 

 by their great length, and by being composed of a number of 

 flattened joints or articulations. These joints are not, however, 



