94 GUIDE TO THE AUSTRALIAN MUSEUM. 



1. — Turbellaria, which possess a digestive cavity, have the 

 skin covered with cilia, and are non-parasitic. This order 

 includes the Planarian and Nemertean worms, the former 

 of which exist in the sea, in fresh water, and in damp forest 

 lands. (See Case 17.) 



2. — Trematoda, which are usually internal parasitic worms, 

 provided with one, two, or more ventral suckers. The 

 species of this order are numerous ; they are found on the 

 gills of fishes, on Crustacea, and in the blood vessels and 

 intestines of various animals. The Liver-fluke of sheep, 

 Distoma hej^atica^ is perhaps the best known example. (See 

 Case 17.) 



3. — Cestoda, which are internal parasites usually of an elongate 

 and flattened form ; the head is provided with hooks, spines, 

 or suckers ; the digestive cavity is absent. The Tapeworm, 

 Tcr.nia solium is a familiar representative of the order. 

 (See Case 17.) 



Class II.— The NEMATHELMINTHES or Threadworms 

 are mostly internal parasites, many of them too small to be 

 exhibited, except with the aid of a microscope. The "vinegar" 

 and "paste" eels Anguillulce, the Guineaworm Filaria medinensis, 

 and the Tricldna sjnralis, found as a parasite in man and causing 

 the disease trichinosis, are examples. 



Class III.— The GEPHYREA.— This is a small class 

 formerly associated with the Echinoderms. It comprises 

 marine worms with a cylindrical body, a thick coriaceous skin, 

 unsegmented, but often indistinctly ringed, mouth with or without 

 tentacles, and head, not distinct from the body, often produced into 

 a long proboscis. The following genera are represented in the 

 collection : Sipunculus, Fhascolosoma, BonelUa, Fhymosoma, and 

 PJioronis. (See Case 17.) 



Class IV.— The ANNELIDA.— In this class there are four 

 orders: — (See Case 17.) 



1. Hirudinea, including the leeches, and composed mostly 

 of aquatic animals provided with a sucking disc at one or 

 both ends of the body. The Hirudo quinquestriata, or 

 Medicinal Leech, is an example of this order. 



