34 CLASSIFICATION OF WOEMS. 



The Vermes are divided into three classes : — 

 (i) PlatyJielminfhes. (ii) Nemathelminthes. (iii) Annelida. 



(i) The Platyhelminthes are Flat -worms with elongated 

 bodies and cerebral ganglia ; they are provided . with suckers 

 and hooks. Most are hermaphrodites. They are grouped in 

 four orders : — 



(a) Turlellaria (Planarians, &c.) These are of no agricul- 

 tural importance. 



(h) Trematoda (Flukes). Parasitic, and produce various 

 diseases in animals. 



(c) Oestoda (Tapeworms). Purely parasitic, often with com- 



plicated life-history. 



(d) Nemertini. Parasitic only in Mollusca and Crustacea, 

 (ii) The Nemathelminthes are Eound-worms, with tubular, 



cylindrical, or filiform bodies. The anterior or head region is 

 either armed with hooks or papillae, and there may be hooks on 

 the posterior end of the male. Sexes separated. There are two 

 orders — 



(a) Nematoda (Thread-worms). Many of these round thread- 

 worms are most injurious to animals, living as parasites 

 in various parts of the body. 

 (6) Acanthocephala, a small group of Nemathelminthes found 



parasitic in man and some animals, 

 (iii) The Annelida are segmented worms with a so-called 

 "brain," an oesophageal nerve-ring and a ventral nerve-chord, 

 and a closed vascular or blood system. They form the highest 

 group of worms, and are, as a rule, free living ; some are par- 

 tially parasitic. There are three sub-classes : — 



Sub-class A. Ch^topoda. Pree annelids, with paired tufts of 

 setae or bristles on the segments ; distinct head, tentacles, 

 and gills. 



Order i. Polychmtm. Marine worms only. 

 Order ii. OUgochcetce. Earth-worms, &c. 

 Sub-class B. Gephteea. — ^All this sub-class are marine, and 



so of no importance here. 

 Sub-class C. HiEUDiNEA (Leeches). — These are partially para- 



