TREMATODA. 565 



practical problem of the prevention of " staggers." Others 

 of the same family of parasites are quite as remarkable, in 

 giving a preference to the alimentary canal of fishes. The 

 Echinorhynchus is developed in the canal of the Flounder, 

 Tricenopliorus nodulus in the liver of the Salmon, attain- 

 ing a more perfect development in the alimentary canal of 

 the Perch and Pike. Another, found in the Stickleback, 

 becomes changed in the intestines of water birds, which 

 devour these fish ; and thus, by careful and repeated 

 observations with the microscope, the connexion existing 

 between the Cystic and Cestoid Entozoa have been most 

 satisfactorily established. 



The Fluke belongs to the order Trematoda, which 

 signifies that they are internal parasites, suctorial worms, 

 or helminths ; they are all usually visible to the naked 

 eye, although a few of the smallest scarcely exceed 1-1 00th 

 of an inch in length ; many are larger, and the species best 

 known, Fasciola Jiepatica, attains to an inch or more in 

 length. The Fluke shown in Plate IV. No. 103, is cone- 

 shaped : it is the Amphistome conicum of liudolphi. This 

 parasite is common in oxen, sheep, and deer, and it has also 

 been found in the Dorcas antelope. It almost invariably 

 takes up its abode in the first stomach, or rumen, attaching 

 itself to the walls of the interior. 1 In the full-grown state 

 it never exceeds half an inch in length ; in our plate it is 

 represented magnified. On closer inspection it will be seen 

 that the animal is furnished with two pores or suckers, one 

 at either extremity of the body, the lower being by far the 

 larger of the two. By means of the latter the Amphistome 

 anchors itself to the papillated folds of the paunch, or first 

 stomach, as this organ is improperly called. 



In the figure the oral sucker at the anterior end, or head, 

 leads into a narrow tube, forming the throat or oesophagus, 

 and this speedily divides, or rather widens out, into a pair 

 of capacious canals. These cavities are correctly regarded 



(1) The larval condition of Amphisloma in all probability lives in or upon the 

 body of snails. This we infer from the circumstance that the larvae, cercarice, 

 of a closely allied species, the Amphistomasubdavatum, which is known to infest 

 i he alimentary canal of frogs and newts, have been also found on the surface of 

 t he body of the Planorbis by ourselves, whilst Van Beneden discovered the 

 larvae in a species of Cyclas. The cercarice, larvae, are taken, it is supposed, by 

 the cattle while drinking. They then attach themselves to the walls of the 

 stomach, where they soon complete their further stages of development. 



