6o6 



NATURE 



[Oct. 19, 1882 



species of Ceriornis has its home. This is Blyth's 

 Tragopan (C. blythi), first discovered in the Mishmi 

 Hills by the late Dr. Jordin during his excursion to 

 Assam in 1869, and subsequently met with by Major 

 Godwin-Austen in the Naga Hills, south of the Brahma- 

 putra. Blyth's Tragopan has likewise been once ex- 

 hibited alive in the Zoological Society's Gardens, an 

 adult male of this fine bird having been presented to the 

 collection by Major Montagu in 1870. Little, however, 

 is yet known of it. 



The fifth and last species of Tragopan, which we now 

 figure (Fig. 25), from an example lately acquired by the 

 Zoological Society, is still more rare and little known than 

 the four above-mentioned members of the genus. Cabot's 

 Tragopan, as it is called, was described in 1857 by the 

 late Mr. Gould, and subsequently figured in his great illus- 

 trated work on the Birds of Asia. Its habitat is South- 

 Eastern China, but little is yet known of its exact range. 

 The only naturalist who has met with it in its native wilds 

 is the celebrated Chinese explorer, M. le Pere David. M. 

 David, in his " Oiseaux de la Chine," tells us that he 

 found this fine Gallinaceous bird rather common in the 

 wooded mountainous range which separates the provinces 

 of Fokien and Kiangsi, when he traversed this district in 

 the autumn of 1873, and obtained many examples for the 

 French National Collection. 



So far as has been recorded, the male specimen of this 

 Tragopan, received by the Zoological Society in April last 

 is the only example that has reached Europe alive. 



THE ROT IN SHEEP, OR THE LIFE-HISTORY 



OF THE LIVER-FLUKE 

 'THE winter of 1879-80 was marked by a widely-spread 

 *■ outbreak of the liver-rot amongst our sheep. The 

 losses during that winter were estimated at three million 

 sheep, or about one-tenth of the total number in the 

 United Kingdom, and during the following winter the 

 losses were equally severe. It had long been known that 

 the disease was due to the presence in large numbers of 

 a parasite called the liver-fluke {Fasciola hepaticd) in 

 the liver of the affected animals, and that the parasite in- 

 vaded sheep or sometimes other animals allowed to feed 

 on wet pastures, and especially on flooded ground. But 

 notwithstanding that the question had been repeatedly 

 investigated by numerous zoologists, including Prof. 

 Leuckart, so well known for his researches on parasites, 

 the manner in which the disease was incurred remained 

 a complete mystery. It was known indeed that the animals 

 most nearly allied to the liver-fluke, the digenetic Trema- 

 todes, presented an alternation of generations, and that 

 they possessed larval forms infesting various species of 

 molluscs. These nurse-forms, as they are called, produce 

 internally larvae, usually tailed, known as cercariae, which 

 leave the nurse and encyst themselves in some other 

 mollusc or in aquatic insect larva;, &c, and remain there 

 quiescent, only reaching maturity if swallowed together 

 with the animal harbouring them by some suitable verte- 

 brate host. Such is a typical instance of the develop- 

 ment of a trematode with alternation of generations, but 

 there is a good deal of variety in the life-histories of the 

 different species. It was supposed that the liver-fluke 

 had a somewhat similar life-history, but all attempts to 

 discover what mollusc served as intermediate host had 

 been fruitless. 



The Royal Agricultural Society of England was in- 

 duced by the heavy losses of sheep in 1879-80 to offer a 

 grant for the investigation of the natural history of this 

 most destructive parasite. I undertook the research, and 

 the results of my work during the summer and autumn of 

 1880 were published in the Journal of the Society for 

 April 1881. Certain slugs had been suggested as pro- 

 bable bearers of the larval form of the liver-fluke, and I 

 was able to show that these conjectures had little evidence 



to support them, and suggested that Limnaus truncatulus 

 was really the intermediate host, or at least one of the 

 intermediate hosts of the liver-fluke. For on the Earl of 

 Abingdon's estate at Wytham, I examined thoroughly a 

 clearly circumscribed area of infection situated on the 

 side of a hill far above the reach of floods, and found that 

 almost the only species of water-snail occurring on the 

 ground was Limnaus truncatulus, found in a boggy spot. 

 This contained an interesting form of cercaria, produced 

 in a cylindrical redia, or nurse-form provided with di- 

 gestive tract. 



The free cercaria had a body of oval form, about o - 3 

 mm. ( g \; in.) in length, but was of very changeable shape. 

 The two suckers characteristic of the adult forms of 

 the family of the Distomidce were of nearly equal size, 

 the oral sucker about terminal, and the ventral sucker near 

 the middle of the ventral surface. The anterior part of 

 the body was covered, at least in the most mature ex- 

 amples, with exceedingly minute spines. But the most 

 striking character of the cercaria was due to lobed lateral 

 masses extending the whole length of the body on each 

 side of the middle line. These lobed masses were an 

 opaque white from the multitude of granules composing 

 them. The cercaria had a tail, which, when fully ex- 

 tended, was more than twice the length of the body. It 

 was exceedingly active, but soon came to rest, showing a 

 strong tendency to encyst itself on surrounding objects. It 

 contracted so as to assume a rounded form, and exuded a 

 mucous substance, containing numerous opaque granules 

 derived from the lateral masses described, which were thus 

 shown to be a special larval organ, producing the sub- 

 stance of which the cyst was composed. The tail con- 

 tinued to wag violently, and was at length pinched off as 

 it were by the hardening wall of the cyst. The cysts were 

 snowy white by reflected light, but on rupturing them 

 the included larva; was found to be quite transparent. 

 I had a few months previously seen a sheep which I had 

 the best possible reason for knowing to be infected with 

 flukes, wandering over the boggy spot from which the 

 snail containing the cercaria came, and the presence of 

 so highly developed an organ for the production of the sub- 

 stance of the cyst in a cercaria which encysted on any 

 plants at hand, seemed to indicate that here was the 

 cercaria of the liver-fluke, and it has since been proved 

 that such was the case. Moreover, I had collected evi- 

 dence from independent sources, which rendered it pro- 

 bable that the parasite was taken up by the sheep while 

 grazing from the damp roots of grass, most likely in the 

 encysted condition. 



Of this cercaria I wrote at the time as follows : — " The 

 structure and habits of this cercaria render it possible that 

 it may prove to be the larva of Lasciola hepatica, but 

 want of material has prevented my testing the question 

 by giving the cyst to rabbits. I intend, however, to 

 pursue this case further." 



Accordingly, during the summer of 1881, I endeavoured 

 to procure L. truncatulus in order to put my strong sus- 

 picion to the test of experiment. But I was unfortunately 

 unable to find any, even in the localities where I had found 

 it during the previous year. In my search I had on many 

 occasions the skilled assistance of my friend and col- 

 league Mr. W. Hatchett Jackson, but we never found any 

 other trace of this species than the empty shells. The 

 localities for the snail mentioned by Whiteave in his 

 paper on the mollusca inhabiting the neighbourhood of 

 Oxford, were searched, but without success. My friends 

 at a distance were appealed to, but were unable to assist 

 me. There can be little doubt that the freedom of sheep 

 near Oxford from the liver-rot during last winter was 

 directly connected with the real scarcity of this snail. 

 This year, however, there were floods on the Isis in July, 

 and L. truncatulus was brought down by the water in 

 vast quantities, probably from marshy ground far up the 

 river. So numerous were they that I repeatedly obtained 



