ii TREMATODA DIGENEA 63 



to both hosts, and a number of Holostomatidae also pass a sta^e 

 of their development within these Amphibia. Some idea of the 

 extent to which animals, whose habits lead to infection, may be 

 attacked by Trematodes (to say nothing of Cestodes and Nema- 

 todes, which often occur also) may be gathered from the fact that 

 in dissecting a black stork, Nathusius found several hundred 

 Holostomum excavatum and about a hundred Distomum ferox in 

 the small intestine, twenty-two D. Mans in the oesophagus, five 

 others in the stomach, and one D. echinatum in the intestine. 

 Snipe, Woodcock, Sandpipers, Dunlin, Gulls, Bittern, Geese, and 

 Wild Ducks are, to mention a few cases, greatly infested by 

 members of this group. 



The following Trematodes have occurred in man 1 : 



Distomum hepaticum Abild. Distomum pulmonale Balz ( = D. 

 lanceolatum Mehlis. ringeri Cobb., D. wester- 



conju7ictum Cobbold. manni Kerb.). 



spathulatum Leuckart ( = oculi humani Ammon (-D. 



D. sinense Cobb., D. ophthalmobium Dies.). 



japonicitm R. Blanch.).. Monostomum lentis v. Nord. 



rathouisi Poir. (probably = Amphistomum hominis Lewis and 



D. crassum Busk, D. M'Connell. 



buskii Lank.). Bilharzia haematobia Cobb. 

 heterophyes v. Sieb. 



Life-histories of the Digenea. The classification of Trema- 

 todes according to their life-histories, expressed in the divisions 

 Monogenea and Digenea, though a very useful one, breaks down 

 entirely in the case of certain forms. Thus the life-history of 

 Gyrodactylus is probably digenetic rather than monogenetic. Aspi- 

 dogaster conchicola, 2 which lives in the pericardial cavity of the 

 fresh-water mussel (possibly the only case of a Trematode becom- 

 ing normally mature in an Invertebrate host, since other species 

 of Aspidog aster live in Chelonia), produces larvae which enter 

 another Anodonta and develop directly into the sexual form. In 

 other words, Aspidogaster, though structurally a digenetic form, 

 possesses a life-history which is direct and simple, i.e. monogenetic. 



The Holostomatidae, which live in birds of prey and 

 aquatic birds, give rise to eggs from which a minute larva 

 escapes. The fate of this aquatic larva is not directly known, 



I ! Leuckart, Parasiten d. Menschen, " Trematoden, " 1892-94; R. Blanchard, 

 Traitd d. Zool. me'dicale, i. 1889 ; H. B. "Ward, Report for 1894 of Nebraska State 

 Board of Agrie. Lincoln, U.S.A. 1895, p. 225. 



2 Huxley, Anat. of Invert. Animals, 1877, p. 194. 



