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veloped head, haviug four suckers and a crown of about twenty-eight 

 hooks. These heads, when the cysts are fed to dogs, may develop into 

 as many individuals. Most of them will generally die, and only a few 

 of the stronger will develop. Instead of the single worm which the 

 embryo of T. marginata produces, this peculiar species develops mauy 

 from each of its embryos. In this there is a compensation; for while 

 mauy of the T. marginata embryos come to maturity, but one or two of 

 the cmnuri survive, and thus the opportunities for the further perpetu- 

 ation of the species are diminished. 



Duration of development. — Experiments have shown that the embryo 

 may be found in the brain from two to three weeks after feeding, and 

 is then about the size of a mustard seed. Between three and six weeks 

 after feeding the worst symptoms of the disease occur. The coenurus 

 becomes developed iu from two to three months. After this time it 

 continues to grow iu size and in the number of heads for six or eight 

 mouths, when it usually causes the destruction of the affected sheep. 

 "When the developed coenurus is fed to a dog it usually produces adult 

 tape worms within a mouth. 



In the migrations of these parasites many are lost and destroyed. Of 

 the hundreds of eggs which leave the intestines of dogs few reacli the 

 stomach of tlie sheep, and of these still fewer enter the cranium. Of 

 the few which become adult — one or two in each sheep affected — ^but 

 a small percentage nowadays arrive in the dog again. Thus of the 

 thousands of embryos that left the dog but a single coenurus may return. 

 But this coenurus, developing again into several tape-worms, is the 

 source of mauy new embryos for the re-infection of the sheep. 



Disease. — Lambs aud yearling sheep seem to be most liable to infection ; 

 those over two years old seem to possess a degree of immunity. Sheep 

 herded by dogs ; those breeds which eat the grass close to the ground; 

 sheep which drink out of ponds or brooks in which the dogs bathe ; 

 flocks belonging to careless flockmasters, who leave the skulls and vis- 

 cera of slaughtered aud dead sheep strewn through the i)astures, are 

 more liable than others. In short, any of the conditions which help in 

 the distribution of the parasites render sheep more subject to the 

 disease. 



Symptoms and progress. — The symptoms of gid in sheep are depend- 

 ent upon the stage of iuvasiou aud development at which the parasite 

 has arrived. The invasion embraces the period from the time that the 

 embryos have been swallowed to the time that they become partially 

 developed in the brain. The stage of development embraces the re- 

 maining time they jiass in the brain. The stage of invasion generally 

 passes unnoticed. Between the second and third week those animals 

 worst infected — for but few of tliose infected show signs of disease in 

 this stage — show symptoms of inflammation of the brain and surround- 

 ing tissues. It is at this period that the little parasites are active in 

 progressing through the tissues. Dullness, feebleness, heat in the head, 



