become thinner at the place under which the bladder-worm is found, sometimes even as thin as paper.) _Remedies_: Trepanning, as the bladders lie just underneath the roof of the skull. _Prevention_: Reducing the number of sheep-dogs; giving the dogs medicine to rid them of tapeworms in spring and summer; administering a specific to the yearling sheep in July and August, suitable for driving out any tapeworm larvæ which may be present in their intestines; _burning_ (instead of _burying_) the heads of sheep affected with staggers which have died or been slaughtered. It is but rarely that all the larvæ living on the surface of the brain die between the first and second stages of the disease. A sheep affected by gid is therefore almost sure to die, and should be slaughtered as soon as possible. Compare “false gid,” p. 189. The =Minute Tapeworm of the Dog= (_Tænia eckinococcus_) is at most scarcely one-sixth of an inch long, and consists of only three or four joints, often lives in large numbers in the intestine of the dog without injuring its host, but causes huge cysts (from the size of a pigeon’s egg to that of a child’s head) in the liver, lungs, or other organs of man, pig, and ruminants. These cysts are of the type represented on the right of Fig. 138. They may prove fatal, owing to the pressure they exert in the organs containing them and the blood-vessels of the same. The =Expanded Tapeworm= (_Tænia expansa_) lives in the intestine of the ox, where it may attain the length of two feet, while in the intestine of the lamb it reaches at most the length of about nineteen inches. It is sometimes present in large numbers in lambs, causing difficulty of digestion with resulting emaciation, poverty of blood, and even death. Bladder-worm still unknown. ORDER: =Trematoda= (FLUKES). Flattened parasitic worms, tongue-shaped or leaf-shaped, living on or in a host, and provided with one or two ventral suckers. The intestine forks into two branches immediately behind the gullet, and these two divisions in some species (_e.g._ the large liver-fluke) branch again repeatedly in a tree-like fashion. Anus and blood-vessels absent. Almost all flukes are hermaphrodite; they fertilize themselves. All the forms living within a host (_i.e._ endoparasitic forms) lay an immense number of small eggs, from which larvæ are hatched that become asexually reproducing animals. These or their progeny produce once more the sexual form. The development is therefore an example of metagenesis (p. 16), but there is a change of host. Only the two liver-flukes need be dealt with here. The =Large Liver Fluke= (_Distoma hepaticum_),