'208 president's address. 



cavity or pulmouary sac, at the same time losing its cilia and 

 developing on its interior one or more secondary embryos called 

 " rediae." The redia, when mature, is set free from its envelop- 

 ing cyst, bores again into the tissues of the mollusc, and produces 

 a number of tertiary embryos of different kinds called " cercarise" 

 and '' daughter-rediae." The cercaria is a curious tadpole-like 

 creature, with a long tail and an anterior and posterior sucker and 

 a distinct mouth and gullet. Having worked its way once more 

 out of its host, the cercaria leads for a time a free life, swim- 

 ming actively in the water. Then, attaching itself by its suckers 

 to some piece of grass or herbage it casts off or loses by absorp- 

 tion, its tail, and becomes enveloped in a horny capsule or cyst. 

 In this condition it may of course be readily eaten by a browsing 

 sheep, and when taken into the body of that animal speedily 

 assumes its adult form. Dr. Cobbold states that in the season of 

 1830-31 " the estimated deaths of sheep from rot were between 

 one and two millions, representing a money loss of something 

 like four million pounds sterling," and that " in the neighbour- 

 hood of Aries alone, during the year 1812, no less than 300,000 

 sheep perished, and at Mmes and Montpellier 90,000. In the 

 inner departments, during the epidemic of the years 1853-54, 

 many cattle-breeders lost a fourth, a third, and even three- 

 fourths of their flocks. * * * On the estate of Mr. Cramp, 

 of the Isle of Thanet, the rot epidemic of 1824 'swept away 

 £3,000 worth of his sheep in less than three months, compelling 

 him to give up his farm.' Scores of cases are on record whore 

 our English farmers have individually lost three, four, five, six, 

 seven, and even eight hundred sheep in a single season ; and 

 many agriculturalists have thus become completely ruined." 

 These statistics refer chiefly to the first half of the present cen- 

 tury, and since that time much has doubtless been done, by 

 drainage of swampy land, to remedy the evil, for on dry ground 

 it is apparent that the disease cannot maintain itself. 



To follow this part of our subject further would try your 

 patience and carry me far beyond the limits of ray allotted time. 

 Much remains to be done in tracing out the life-histories of tlie 



