1 86 LEISURE-TIME STUDIES. 



strength to sweep away the greatest obstacles man or nature 

 may oppose to its fury. Invest, further, the idea of the single 

 raindrop with time, and the action which appears feeble, if 

 viewed for a single moment, becomes of mighty extent when 

 multiplied into years and centuries. And similarly with the 

 case of the fluke and its neighbour-parasites. A single fluke 

 is of itself an unimportant quantity, but when this quantity 

 becomes multiplied by hundreds, the proverb that " union is 

 strength " receives a new and very decided application. 

 Existing in large numbers within the liver-ducts of the sheep, 

 the flukes cause irritation, and a whole train of symptoms 

 which end usually in starvation and death. Hence the 

 extreme fertility of parasites might well afford a text whereon 

 a sophist might inveigh against the wise regulation of the 

 domain of living nature, were it not that in reality these 

 animals are checked and controlled through the actual com- 

 plexity of their own development. Strange as the statement 

 may seem, it is nevertheless true that Nature appears to 

 offer a premium against the development and increase of 

 these and other parasites, through their having to undergo a 

 series of very striking changes on the way to maturity. The 

 parasite's path to adult life may truly be described as 

 chequered in the highest degree. There are numerous pit- 

 falls and snares laid for its reception, and for the extinction 

 of its young life ; and the " struggle for existence " in the 

 present case is not only fierce, but, in the case of a very 

 large majority of the combatants, utterly hopeless. 



Let us briefly trace the life-history of a fluke by way of 

 practical illustration of these latter remarks. From each 

 individual fluke residing within the body of its sheep-host, 

 hundreds of eggs are discharged. Each egg undergoes a 

 preliminary process of development, and from the eggs 

 which escape into water, little free-swimming bodies are 

 liberated. These minute living particles are young or em- 

 bryo flukes. Each resembles an inverted cone in shape, 

 and swims rapidly through the water by aid of the micro- 

 scopic filaments which fringe its body. It is clear that such 



