252 SELECTED NOTES FROM 



At another part of the same work, ^' Animal Parasites and 

 Messmates," the author describes the development of the Fluke, 

 saying that the eggs, which are extremely numerous, each hatch 

 into a ciliated infusorial (which, however, he does not identify with 

 Opalina). These infusorial organisms swim about freely for a few 

 days, then lose their cilia, and crawl about slowly. They have all 

 been deposited by the parent Fluke, either during its lifetime, or 

 by being liberated by its decomposition when dead. They are 

 dispersed in various ways and many perish, but some gain an entry 

 into the body of what is to serve as their host, where they undergo 

 further development. This host is generally a Mollusc, in whose 

 body the larva develops other larvae of altered character, which are 

 now called Ce?'carzce. 



These escape from the body of the Mollusc, which has been 

 their intermediate host, and again swim freely in the water. After- 

 wards, they again enter the bodies of other Molluscs, a feat 

 which they accomplish by means of a boring-apparatus, and having 

 previously cast off their tails, they become encysted under the 

 skin. Here they change from the larva into the pupa state, and 

 are afterwards transferred with the fodder or drink to the digestive 

 organs of their future victims. The gastric juice dissolves the 

 cyst and sets free its inhabitant, which is now able to make its 

 way into various parts of the digestive organs, and when mature 

 discharges its eggs, to again go the same wonderful round. 



With regard to OpalinidcE^ mentioned at the beginning of this 

 article, Savile Kent states that there would appear to be a relation- 

 ship between them and a certain stage of the development of some 

 Cestoid worms, but that at present there is not sufficient evidence 

 of their identity, 



I will finish by quoting Dr. Cobbold's estimate of the possible 

 number of these parasites which may be derived from one 

 diseased sheep. 



He says : — " A single sheep may harbour i,ooo Flukes ; each 

 Fluke will develop 10,000 to 40,000 eggs ; and each egg may give 

 rise to 370 Cercarice. 



" ThuS;, one Fluke might originate between three and four 

 millions of these life-forms, and one sheep might be the means of 

 producing at least 3,000,000,000 (three thousand milHons). 



"By far the larger portion of this immense number perish 

 before coming to maturity ; but still enough of them survive to 

 destroy thousands of sheep annually." 



Geo. D. Brown. 



