330 



SCIENCE. 



[Vol. I., No. 12. 



LIFE-HISTORY OF THE LIVER-FLUKE. 



Peof. a. p. Thomas, now of Auckland, New 

 Zealand, has published in full the results of his valua- 

 ble and important researches on the development of 

 the liver-parasites, which produce the so-called 'rot,' 

 — a disease that is especially fatal to sheep, but some- 

 times occurs in man. It is estimated to have occa- 

 sioned the loss of some 3,000,000 sheep in Great 

 Britain during the winter of 1879-80. Leuckart has 

 also studied this subject, and reported his observa- 

 tions in the Zoolorjischen anzeic/er for Oct., 9, 1882. 

 Thomas's results, as given in the Quarterly journal of 

 microscopical science for January, 1883, are remarka- 



the time needed to produce the embryos: hence a 

 field once infested remains dangerous for a long time. 

 The embryo enlarges at the expense of the nutritive 

 material (so-called yolk-cells, though they have noth- 

 ing to do with the yolk), and, when mature, bursts 

 open the operculum of the egg-shell, and immediately 

 begins swimming freely in the water. Its form is an 

 elongated cone (0.13 mm. long), with roimded apex, 

 as is shown in fig. A of the accompanying cut. The 

 base of the cone is directed forwards, and in its 

 centre is a short retractile head-papilla, pr. The 

 whole surface is covered with cilia, which are borne 

 by the large ectodermal cells. In the interior are two 

 eyes, oc, and other structures, which are very briefly 



Explanation of fiqdres. — A, embryo; B, sporocyst; C, redia; D, cercaria; E, young sporocyst; F, cyetogenous cell ; G-, pod 

 cell from cercaria. oc, ocelli; sp, spores; i?, redia; pft, pharynx; q, collar of redia; c, cystogenous cells; s, sucker. 



bly complete; and, as they are of general interest, we 

 present an abstract of thera. 



The adult worm (Distoraum liepaticum) infests the 

 liver of mannnals. It discharges its eggs into the bile- 

 ducts, which they sometimes clog. The eggs then 

 pass into the intestines, and may be found abitn- 

 dantly in the droppings of the host. The number of 

 eggs emitted by a single fluke may be safely estimated 

 at scvei'al hundred thousands. Segmentation of the 

 ovum occurs in the body of the host; but the further 

 development being dependent on a lower temperature 

 than that of the mammalian body, and on moisture, 

 can proceed only after the eggs are discharged. 23°- 

 26° C. is most favorable, the embryo being formed 

 in about three weeks. At a lower temperature, the 

 development is prolonged ; but, under the same con- 

 ditions, the individual eggs vary enormously as to 



described, and call for further study. The embryo 

 is exceedingly active, swimming about like an infu- 

 sorian, though more rapidly. When it meets a Lym- 

 naeus trunculatiis (a common snail), its first host, it 

 presses the head-papilla against the surface of the 

 snail, and begins spinning around its axis, and work- 

 ing its body, until the tissues of the snail are forced 

 apart, leaving a gap through which the embryo 

 squeezes its way into its host. The embryo appears 

 to have some means of in-stinctlvely recognizing the 

 trunculatns, for it does not attack other species. It 

 cannot live much more than about twelve hours in 

 water, and it usually gets into a snail within eight 

 hours. 



In the snail it changes into a sporocyst, which, 

 during warm summer weather, may reach its full size 

 within a fortnight; but in autumn twice that time 



