4 INTRODUCTION 



I. FLUKES. TREMATODA. This group embraces several fami- 

 lies of parenchymatous worms. The various species exhibit 

 one or more suckers, which the older naturalists regarded as so 

 many mouths or perforations. Hence the ordinal title. The 

 term fluke is of Saxon origin, meaning anything flat. Thus, 

 it has been applied to sole-fish or flounders, to the flattened 

 halves of the tail of cetaceans, to the blades of anchors, and so 

 forth. Although the common liver fluke is flat, many species 

 of the order are round, biconvex, or even filiform organisms. 

 I recognise six families : Monostomida, Distomidte, Amphisto- 

 midfSj Tristomida, Polystomidte, and Gyrodactylida. Most of 

 the species are entozoal; but many adhere to the surface of 

 the body of piscine hosts. 



II. TAPEWORMS. CESTODA. This comprises not only the 

 tapeworms, but also the measles and other bladder-worms or 

 cystic Entozoa of the old authors (Cystica). The Greek word 

 kestos means a band or girdle ; hence the ordinal term above 

 given. The bladder- worms, including Hydatids, Cysticerci, 

 &c., are the larval stages of growth of various tapeworms. 

 The further reduction of this order into sub-orders or families 

 requires careful attention. At present we have Taniadte, A<-n- 

 thotteniada, Dibothrida (=Bothriocephalid<e), Diphyllobothrida, 

 Tetrarliynchida, and Tetraphyllobothridte. All the genera and 

 species are entozoal. The proposal to separate the snouted 

 or proboscidiform tapeworms (RJnjnchotaniada) from those in 

 which the rostellum is absent (Arhynchotaniada) does not 

 recommend itself to my judgment. 



III. ROUNDWORMS. NEMATODA. This series comprises not 

 only lumbricoid or roundworms proper, but also threadworms. 

 The term derives its origin from the Greek word nema, signify- 

 ing a thread. It .likewise includes the strongyles, the term 

 strongulos meaning round or cylindrical. This is a very extensive 

 group whose parasitic members are strictly entozoal, whilst the 

 non -parasitic forms are either entirely free or they infest plants. 

 Some of the so-called free nematoids live in the slime of 

 animals. The artificial classification by Schneider, based on the 

 muscular system, places these parasites in three well-marked 

 groups, but I think it a disadvantage to separate widely many 

 really closely allied forms. Thus, in his Polymyarii we have 

 the genus Eustrongylus, and in his Meromyarii the Strongyli 

 proper. Most of the genera may be fairly included in the 

 following families : Ascarida, Cheiracantliidce , Cucullanida, 



