Class IV.— VERMES (WORMS). 



Characters. — Vermes form a "heterogenous mob" of animals amongst 

 the lowest Metazoa, with no well-defined characters. The class Vermes 

 includes nearly all the invertebrates that cannot be placed amongst 

 Protozoa, Porifera, Coelenterates, Echinoderms, Molluscs, or Arthropods. 

 Each of the following sub-divisions of Vermes is, however, probably a class 

 equivalent to the class Vertebrata, or to any of the just-mentioned 

 classes : — 



I. PLATYHELMINTHES (Flat Worms).— Flattened ; elongated ; un- 

 segmented. No distinct body cavity. Excretory system in the form of 

 longitudinal vessels, with greatly ramifying branches. No ventral nerve 

 cord. 



1. TuRBELLARiA (Planarije). — Non-parasitic. Soft skin externally ciliated, 



Mouth and gut. No anus. Often with a protrusible pharynx 

 (proboscis), e.g. Planaria, Mesostomum. 



2. Nemertea. — Non-parasitic. External cilia. Protrusible proboscis, in 



a sheath, independent of the gut. Nervous system in the form of two 

 supra-cesophageal ganglia, and two lateral nerve curds, e.g. Nemertes. 



3. Tebmatoda (Flukes). — Ecto- parasitic or endo -parasitic. Skin not 



ciliated in adult. Sucker at anterior and (usually) at posterior end. 

 Hermaphrodite. Life history, either complicated, and with alter- 

 nation of generations (when endo-parasitic), or simple (when ecto- 

 parasitic). e.g. Distomum (liver iluke, the cause of rot in sheep). 



4. Cestoidea (Tape Worms). — Endo-parasitic. No mouth or gut. Adult 



is jointed, first joint being the " head," from which are budded off 

 the remaining (generative) joints. Head with suckers and hooks. 

 Hermaphrodite. Complicated life history, with alternation of 

 generations, e.g. Taenia (tape-worm), Bothriocephalus. 



II. NEMATHELMINTHES (Nematoidea, Bound or Thread Worms).— 

 Eounded; of ten thread-like ; elongated; thick horny skin. Intestine straight. 

 Anus. Body-cavity. Free or parasitic. Mostly disecious. e.g. Trichina 

 (the worm of trichinosis). 



III. ROTIFEEA (Rotatoria, Wheel Animalcules). — Moiith surrounded 

 by a ciliated disc (wheel organ). Excretory system in the form of tubes 

 opening into body cavity, and into a cloaca. Males smaller and less 

 developed than females, e.g. Eotifer. 



IV. GEPHYEEA (Spoon Worms). — Unsegmented. Excretory organs of 

 the kind found in Chsetopods, as well as those in Eotifers. e.g. Bonellia, 

 which exhibits sexual dimorphism, females being larger and more numerous 

 than males, which are carried about by the females. 



V. CH^TOPODA (Annelida, Bristle-footed or Einged Worms).— Non- 

 parasitic. Segmented. Nervous system of paired supra-oesophageal ganglia, 



