TREMATODA 



557 



Jehan de Brie discovered the liver-fluke in the sheep, which was sub- 

 sequently described by Gabucinus in 1547; but it was not till the 

 time of O. F. Miiller, in 1777, that any accurate idea of their form was 

 obtained. Zeder in i"oo made the first attempt to classify parasitic 

 worms, calling the Trematodes ' sucking-worms ' ; while in 1808 

 Rudolphi invented the name of the class, deriving it from the Greek 

 Tprj/jLarcoSr)^ which means, ' pierced by holes.' After this date come 

 many observers, among whom may be mentioned Laurer (whose 



canal still bears his name) in 

 1830, van Beneden in 1858, and 

 Leuckart in 1867 (who divided 

 them into Distomea and Poly- 

 storpea), and Thomas in 1883, 



Fig, 210. — Diagram of a Type of 

 THE Female Generative Appar- 

 atus OF A Trematode. 



(After Stiles.) 

 I, Ovary; 2, uterus; 3, shell gland; 

 4, Gotype; 5, ovarian duct; 6, Lau- 

 rer's canal; 7, vitellarian duct. 



Fig. 211. — Diagram of Another 

 Type of the Female Genera 

 tive Apparatus of a Trematode. 



I, Ovary; 2, ovarian duct; 3, shell 

 gland ; 4, ootype ; 5, uterus ; 6, 

 Laurer's canal ; 7, vitellarian duct ; 

 8, receptaculum seminis. 



who worked out the development of Fasciola hcpatica. In 1892 

 Monticelli revived an older classification of the group by Burmeister 

 into three orders. 



In 1899 LoOss completely revolutionized the whole classification. 

 His work has since been extended by Leiper, Odhner, Llihe, and 

 others. Of recent years our knowledge of the life-history of these 

 parasites has been extended in a remarkable manner by Leiper and 

 numerous Japanese observers. 



Morphology. — In shape the Trematoda are generally leaf-like or tongue- 

 shaped, and but rarely cylindrical. They are provided with a cuticle, which 

 may have spine-like scales, and with one or two suckers, oral and ventral 

 (often called the ' acetabulum '), which are capable of fixing the parasites by 

 the action of their equatorial, meridional, and radial muscular fibres to the 

 lining of the alimentary canal, or such other organ as they may inhabit. 



The mouth lies in the oral sucker, and leads to a pharynx. The oesophagus 

 may be short or long, with or without a sphincter muscle, and is often pro- 

 vided with unicellular salivary glands. The intestinal tubules, which may 

 be branched or simple, end blindly, there being no anal aperture. The food 

 is composed of epithelial cells and blood. 



The excretory system is well developed, commencing in special cells pro- 

 vided with cilia (flame cells), which communicate with excretory capillaries. 

 These open into canals, which anastomose freely, and then join the gathering 

 tubes, which open into an excretory vesicle. This vesicle, which may be long 



