144 PL A T YHELMINTHES. 



Distomum belongs to the phylum PLATYH EL- 

 MI NTH ES because of its flattened unsegmented body, 

 its simple alimentary canal with no anus, and its meso- 

 dermic parenchyma with flame -cell excretory organs. It 

 belongs to the class Trematoda because of its parasitic 

 habit with suckers, thick hooked cuticle and complex sexual 

 organs, 



II.— TiENIA. 



Phylum - - Platyhelminthes. 

 Class - - - Cestoda. 



Taenia solium is a common tape-worm inhabiting 



the intestine of the human subject. It is of great length 



E t rnai (often nine to ten feet) and flattened dorso- 



ventrally. The anterior end is extremely small, 



terminating in a knob called the head. The 



body enlarges gradually backwards, and it is broadest at the 



extreme hind-end. It is produced anteriorly into a process 



or rostellum which bears a ring of (22-32) hooks and behind 



them there are four large suckers. A little way behind the 



head there appear transverse constrictions running across 



the body. These get wider apart and deeper towards the 



hind-end, and partially divide the body into a series of 



sections known as proglottides. There may be about 850 



proglottides, of which the broadest are about \ inch across. 



There is no mouth, no alimentary system, and no 



sensory organs, but the nervous and excretory systems 



are well developed. There is a nerve-ring in the 



head with two lateral ganglia giving branches to 



the suckers. There j)ass backwards from them a pair of 



lateral nerves which run throughout the length of the body. 



The excretory system has also a ring in the head and 



four longitudinal ducts. The dorsal and ventral pair do 



not proceed far, but the lateral ducts pass down the entire 



length of the body just inside the nerves. In the posterior 



Excretor P^^^ ^^ ^^^^ proglottis they are connected by a 



■ transverse duct, and in the last proglottis this duct 



opens medially through a contractile vesicle to the exterior. 



Numerous secondary branches break up in the parenchyma 



and terminate in " flame-cells." 



