322 PLATTHELMINTHES. 



Distomnm. Median sticker approached to the anterior one. If. licpaticum L, 

 Liver fluke. With conical anterior end. and numerous spine-like prominences 

 on the surface of the broad leaf-shaped body, which is about 30 mm. long. 

 Lives in the bile-clu^ts of sheep and other domestic animals, and produces 

 the liver disease of the sheep. It is occasionally found in Man, and bores its 

 way into the portal vein and into the system of the vena cava. The elongated 

 embryo only develops after the egg has remained a long time in water ; it has 

 a continuous ciliated envelope with an X- shaped eye-spot. E. Leuckart's re- 

 searches have rendered it probable that the development is passed through in 

 the young Limnceits pereyer and truncatulus, that here the embryo becomes a 

 Sporocyst. and that this produces EC dice, in which it is supposed that tailless 

 Distom-ca arise. 



[The life-history of the liver-fluke has been completely worked out by A. P. 

 Thomas (Quart. Journal of Mic-roscoplcal Set. 1883, pp. 99133). He has 

 shown that the ciliated embryo passes into Limnceits tmncatuliis, and there 

 gives rise to a sporocyst which produces rediae. The redice produce more 

 re dice or Ccrcarice. The Cercaritf. which are provided with long tails, leave 

 the host (Limncens trimcatttlvs), swim about for a short time in the water, and 

 encyst on foreign objects, e.g. blades of grass. In this condition they are eaten 

 by the sheep.] 



D. crassum Busk., in the alimentary canal of the Chinese, one to two inches 

 in length, and half-inch broad, without spinous prominences, with a simple 

 forked intestine. D. lanceolatum Mehlis. Body elongated into the form of a 

 lancet, 8 9 m.m. long, lives in the same place with D. liepaticum. The embryo 

 develops at first in water, is pear-shaped, and only ciliated on the anterior half 

 of the body, bears a styliform spine on the projecting apex. D. oplithalmoMum 

 Dies. A doubtful species of which'only four specimens have been observed in tho 

 lens capsule of a nine-months' child. D. lieteropliycs Bllh. v Sieb. 1 1'5 mm. 

 long, in the alimentary canal of man in Egypt. D. goliath van Ben., 80 mm. 

 long, in Pterobalesna. Numerous species live in the alimentary canal, lungs, 

 and bladder of the frog. Distomun filicolle Eud. (D. Olieni Roll) in pairs in 

 the mucous sacs in the branchial cavity of Brama Raji. The one individual is 

 cylindrical and narrow, and produces spermatozoa ; the other is swollen in the 

 middle and posterior region of the body, and is filled with eggs. The dissimilar 

 development of the two individuals is probably due to the fact that copulation 

 only leads to the fertilization of one of them, which alone is able to perform 

 the female sexual functions. I), licematobium. Bilh. v. Sieb. (Gynwcopliorus 

 Dies) (fig. 257). Body elongated ; sexes separate. The female is slender and 

 cylindrical. The male has powerful suckers, and the lateral margins of the 

 body arc bent round o as to form a groove, the canalis gynascophorus, for the 

 reception of the female. They live in pairs in the portal vein, and in the veins 

 of the intestine and of the bladder of man in Abyssinia. According to Cobbold, 

 the embryos are ciliated, and possess a tolerably well dereloped excretory 

 system. By the deposition of masses of their eggs in the vessels of the mucous 

 membrane of the ureter, bladder, a ad great intestine, inflammation is set up, 

 which may cause hrcmaturia. 



(2) Sub-order: Polystomea. Trematodes with two small lateral 

 suckers at the anterior end, and one or more posterior suckers, to 

 which two large cliitinous hooks are often added. In exceptional 



