234 DISEASES DUE TO HELMINTHS 



The muscular fibres are longitudinal. There are no cilia. 



The excretory system consists of a simple bilateral symmetrical 

 system of tubules opening into a single excretory pore on the ventral 

 surface of the body in the middle line. 



The sexes are separate. 



The Nematoda always have an alimentary canal. Nearly all those 

 found in man are from this class. 



The Nematomorpha have an alimentary canal which atrophies in 

 the adult. 



The Acanthocephala have no alimentary canal. 



Nemathelmia pathogenic to man will be dealt with later. 



THE PLATYHELMIA HAVE THREE CLASSES. 



Glass (i) The Turbellaria. Flat worms, ciliated^ free-living. 



They are not important for man. 

 Class (2) The Trematoda. Flat worms with an alimentary canal. 



They are parasitic to man. 

 Class (3) The Castoida. Flat worms without an alimentary canal. 



They are parasitic to man. 



I TREMATODA PATHOGENIC TO MAN. 



THE MORPHOLOGY. 



Their average length is ^ in., but their extremes are i'2^ to 3 in. 



They are leaf-like or tongue-shaped, rarely cylindrical. 



There are two suckers, one ventral and one oral, which fix the 

 parasites to the lining of the intestine or other organ. 



The mouth lies in the oral sucker. 



The oesophagus may be long or short, and often has unicellular 

 salivary glands. 



The intestine is branched or simple and ends blindly. 



There is no anus. 



The testes may be branched, or simple, or lobed. 



The ovary may be branched, simple, or lobed, and is usually in 

 front of the testes. 



These characteristics are used to differentiate the species as shown 

 in the preceding table of the Fasciolidas. 



The genital pore is usually near the ventral sucker. 



The cirrus pouch lies behind the genital pore and is present in 

 some as a muscular collar which, when it contracts, inverts by its 

 spines the canal they surround and thus gives an erectile organ which 

 comes out of the genital pore. 



The yolk glands, also used to dififerentiate the species, are arranged 

 in one of three ways, viz. : — 



In the middle third of the body placed laterally. 

 In the posterior third of the body placed laterally. 



