322 PLATYHELMIXTHES. 



Dhtonwm. Median sucker approached to the anterior one. D. hepaticum L. 

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

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

 Lives in the bile-ducts 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. K. Leuckart's re- 

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

 the young Linuueux pereycr and trtuiratiilux. that here the embryo becomes a 

 Xjiurocyxt. and that this produces Redia-, in which it is supposed that tailless 

 Distmnc'd arise. 



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

 Thomas (Quart. Journal of Microscopical Xci. 1883, pp. ( J!) 133). He has 

 shown that the ciliated embryo passes into Limitceux triincatuhis, and there 

 gives rise to a sparocyst which produces recliae. The rrtl'ur produce more 

 n-dia or Cercar'ue. The Cercarier, which are provided with long tails, leave 

 the host (Limnceiis tiiincatvlus), swim about for a short time in the water, and 

 encyst on foreign objects, e.ij. 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. lanccoliitum Mehlis. Body elongated into the form of a 

 lancet, 8 9 m.m. long, lives in the same place with 2). lii'patlcinn. 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. op7i-thalimi>bium 

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

 lens capsule of a nine-months' child. ]). lieteropliyes Bilh. v Sieb. 1 1*5 mm. 

 long, in the alimentary canal of man in Egypt. 1). i/oHatli van Ben., 80 mm. 

 long, in Pti'rolaltciui. Numerous species live in the alimentary canal, lungs, 

 and bladder of the frog. Digtomun JUicolle End. (JJ. Okt-nl Ku'll) 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. J). lirrmatoliiinn. Bilh. v. Sieb. (Gyncecqpkorus 

 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 are bent round so as to form a groove, the canalis gynrecophorus, 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 developed excretory 

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

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

 which may cause hfematuria. 



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

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

 which two large chitinous hooks are often added. In exceptional 



