ON ANIMAL PARASITES. 10 L 



length, while others of them are microscopic. The sexes are- 

 imited in the same animal. Unlike the tape-worms, the flukes 

 are never " cystic," the larvae usually being found free and swim- 

 ming in fresh water ; but, on the whole, the source of these worms, 

 and tlie complete stages of their development, is as yet but little 

 understood. There are varieties of the parasite. The common 

 ^iike, Fasciola hepatica, infests most ruminants, including antelopes 

 and deer ; and it has also been found in the horse, the ass, the 

 hare, and the rabbit. It is a rare guest in the ox, but very often 

 infests the liver of the sheep in great numbers, when it gives rise 

 to the disease termed the " rot." The treatment for this is the 

 immediate removal of the sheep to sound pasture, where they 

 should be well fed with dry, nourishing food, with a free allowance 

 of salt and sulphate of iron, and, if needful, a purgative to keep 

 the digestive organs in good order. The lancet-shaped fluke,. 

 Distoma lanceolaiicm, is a smaller one found in the ox more f re- 

 ([uently than in any other host, but occasionally met with in the 

 sheep, and more rarely in red and fallow deer. The cone- 

 shaped fluke, Amphistoma conicum, is another small one, and is 

 not only found in cattle, but in the sheep, the goat, red deer, roe, 

 and fallow deer, the elk, and certain species of antelope. A 

 species of the Amphistomes resides in the frog, and its larvae 

 either take up their abode in or dwell upon at least three different 

 species of water snails. From this, and the fact that the larval 

 Trematode is known as the free swimming Carcarea diphcotylca, 

 it would appear to be pretty well established that cattle and other 

 ruminating animals become infested with flukes in a direct 

 manner, when they drink from pools and even running streams. 



Thorn-headed, Worms (Acanthocephala). — The parasites of this 

 class are represented by a rare worm (Echinorhpnchus gigas) 

 which infests the intestinal canal of the pig, and also that of 

 some birds, fishes, and other vertebrate animals. Like the 

 Tcenia, this worm is developed within a hooked embryo, from 

 which it is secondarily produced. 



Hair- Worms (Gordiacea). — These are small thread-like para- 

 sites, which in the young state inhabit the bodies of various 

 insects, chiefly of beetles and grasshoppers. Others of them 

 infest the livers of herring and fresh-water pike. The embryo 

 of Gordius is armed with booklets, and at first leads a free life,, 

 but soon penetrates the larvae of some aquatic insect and becomes 

 encysted. The adult form possesses a mouth and alimentary 

 canal, and the sexes are distinct. The parasite leaves the body 

 of its host in order to breed. 



Thread Worms or Round Worms (Nematoda). — Most of this 

 order, thougli not all of them, are internal parasites in man and 

 in many other vertebrate animals. Chief amongst the parasitic 

 iSTematodes are the Trichina, the Guinea-worm, the Strongyle, the 



