20 THE WOMBAT. 



parasitical worms alone involves the contemplation of many- 

 curious phases of organic existence. Nothing will illustrate 

 this better than the life-history of the " liver fluke." It is 

 over forty years since this disease was introduced into Victoria 

 by some imported rams. Until quite recently it was a con- 

 stant puzzle to everyone, and it was the researches of Thomas 

 in England, and Leuchart in Germany that cleared up the 

 mystery. 



The adult fluke belongs to a division called "flat worms," 

 which includes some of the worst of parasites, such as the 

 tape-worm. The ova deposited by the adult fluke pass out 

 in the faeces, and are sometimes carried into water. There 

 they hatch out at a temperature of from 74° F. to 78 F. 

 Now the little embryo can live and swim about for a few days,, 

 but before it can develope further it must reach one particular 

 kind of snail. If it does not do so it dies. After undergoing 

 a certain development in the lung chamber of the snail it 

 again comes forth, fixes itself upon some submerged grass or 

 plant leaf, throws off its tail (which it had used for swimming), 

 and forms a little white cyst, which protects it when the water 

 dries up. While the ground remains damp the cercaria, as it 

 is called, retains its vitality, and if eaten by sheep the cyst is 

 dissolved, and the worm, thus set at liberty , finds its way,, 

 most likely up the bile-duct, into the liver, and there its life- 

 history is complete. 



Natural History as a Science. 



As a science natural history certainly stands well to the 

 front. In 1831 the memorable voyage of the " Beagle," a 

 barque of 242 tons, commenced from Devonport to complete 

 the survey of Patagonia, Tierra del Fuego, Chili, Peru and 

 some Pacific islands, and to carry out a series of chronometrical 

 observations throughout the world. On board was Charles 

 Darwin, who was chosen as naturalist under the recommend- 

 ation of Professor Henslow, who told Captain Fitzroy that he 

 was a young man extremely fond of geology and, indeed, all 

 branches of natural history. During the voyage Darwin 

 collected material which, through his own ardent interpretation, 

 has revolutionised not only half a dozen sciences, but the whole 

 current of mental life of thinking men. His observations on 

 the structure and formation of coral reefs, and on the proofs of 

 recent elevation on the coast of Chili, as well as on volcanic 

 islands, placed quite a different complexion on geological ideas. 

 Darwin was certainly the greatest naturalist, and probably 

 the greatest original thinker, that ever lived. It was his studies 

 in natural history that brought to light the marvellous law of 

 evolution, and since his day it is pleasing to see such men as 

 Sir John Lubbock, Lord Kelvin, and Herbert Spencer following 

 in his footsteps. 



