Thomas Carolan, age 14, of Bridgeport, CN for his question:
What are the animals called flukes?
Not all the animals are as cute as kittens Or as docile as dogs. There are also tigers. But man, the hunter, learned long ago how to protect himself and his family from these large menace. The tiny flukes are another matter. They are parasites often more deadly than tigers. Mankind has had to use very different hunting skills to cope with them.
The animal phylum platythelminthes meaning the flatworms includes some 6000 species, and the count is far from complete. A few giants measure almost an inch, but most of them are microscopic. All of them are soft bodied animals without bones, circulatory or breathing systems. They are equipped with cukers or hooks, and some types have both.
The big phylum is divided into three classes. Class I includes the true flatworms, which are free living water dwellers. The flukes are in Class II, and the tapeworms in Class III, and no member of either of these flatworm classes can make a living for itself. All of them are parasites.
The flukes develop from microscopic eggs through a number of larval stages. The four different stages in the life cyc1e of a butterfly seem very complex. But some of the flukes pass through half a dozen widely differing stages of development. Some live their whole life cycle in the same host animal. They tend to attack the gill tissues of fishy the skin or internal organs of reptiles and other cold blooded animals.
We know of some 3000 different flukes, each with his own life story. Most of them must change fry one host to another as they develop from stage to stage. The eggs of one fluke must find a certain snail before they can become larvae, and the larvae must find a certain species of fish in order to reach the next stage of development. The fish and the snail are called intermediate hosts.
The fluke reaches its adult stage in a final host., Where it feeds on the specific tissue it needs to mature and produce eggs. The final host may be man or some wild or domestic animal. In some countries, whole populations are weakened by liver flukes which are eaten in raw fish. In other countries, human beings and animals are attacked by blood flukes and lung flukes which reach their final hosts through careless sewage or impure water supplies.
The fluke, which needb a number of different hosts, has a very hazardous life, and billions of eggs must be produced in order that a few may reach maturity. At a certain stage, the larvae must transfer to a new host within a few hours or perish. Each intemediate host must be a certain species of fish, snail or other animal. However, the fluke may not be so choosy about its final host. At this stage, the lung fluke, for example, will attack the lung tissue of man, cattle and other warm blooded animals.