THE TREMATODA 65 



sucker small ; posterior sucker terminal, usually large, and in front of it 

 fixing papillae may be developed on tlie ventral surface. Amphistomwn, 

 Hud. (Fig. X. 1) ; numerous species in various mammals. A. (Diplo- 

 discus) subclavatum, Goeze, in rectum of Ampliibia (see 30). Gastrothylax, 

 Poir. (Fig. X. 3) ; Homalogaster, Poir. (Fig. X. 2) ; Gastrodiscus, Cobb. ; 

 G. polymastos, Leuckt., in colon of horse. Aspidocotyle, Dies., intestine of 

 fish (Monticelli places the genus in the order Aspidocotylea). FAMILY 2. 

 DISTOMIDAE. The posterior sucker has shifted forwards along the ventral 

 surface, so as to come to lie in the middle of the body, or even in front 

 of this point ; no adhesive papillae, though spines are frequently developed 

 on the surface of the body ; the genital pore is almost always in front of 

 the ventral sucker, usually in the middle line, rarely shifting to the side 

 (see 32, 38, and Fig. XI.). Distomum, Retzius ( = Fasciola, L., in parte), 

 no retractile boring proboscis ; hermaphrodite. The genus has been 

 subdivided into eleven sub-genera. Sg. Cladocoelium, Duj. ; D. hepatic-urn, 

 L., occurs in the bile ducts of various mammals, especially common in sheep, 

 but also in man, kangaroo, ox, etc. The "Liver-fluke" is so commonly 

 taken as a " type " of the Trematoda, that a brief historical account of it 

 may be of interest. 



Being the cause of a disease " sheep-rot " in a domesticated animal 

 it naturally claimed the attention of naturalists and others in early times ; 

 the first account of an epidemic of this disease being given by Gemma 

 (1575) as having occurred in 1552 in Holland. The earlier writers 

 believed the parasite to occur in the blood-vessels of the liver, till Faber 

 (1670) established the fact that it occurs not in the blood-vessels but in 

 the gall bladder and bile ducts and their capillaries (vermis e ductu 

 cystico et poro biliario). Ruysch (1691) gives the first (but extremely 

 poor) picture of the " fluke. " Redi, who was acquainted with quite a 

 number of parasites of birds, mammals, etc., referred to the fluke as 

 vermis vervecini hepatis, and gives a fairly good figure of it. 



Faint inklings of its life-history occur in Gesner's work (1551), where 

 he mentions that in France it had been noticed that in the livers of 

 sheep, which had eaten certain plants growing by the water's side, and 

 termed " duva," small leech-like animals were found, causing a disease in 

 the sheep to which the name "duva" was given. These two uses of the 

 word still exist; douve in modern French is "spearwort," and douve de 

 foie is the liver-fluke. Leeuwenhoek, however, did not connect the fluke 

 with eating, but. believed that the flukes live freely in the water and 

 make their way into the gall bladder of the sheep, while the host is 

 drinking. 



Romberg (1706), on the other hand, who discovered flukes in the calf, 

 regarded them as vermes cucurbitini (a term used at that time for 

 isolated proglottids of Cestodes). Pallas (1760) was the first to add man 

 to the list of hosts. 



The correct name of the liver-fluke is even now a matter of discussion 

 amongst purists of nomenclature. Linnaeus (1746) used the word 

 Fasciola to include the "fluke," a fish Cestode (Schistoceplialus), and a 

 Triclad (Dendrocoetum), under the belief that they were all stages in 

 one life-history, starting with the Planarian ; and to this assemblage gave 



