Introduction
The trematodes are flatworms which are of great importance in tropical pathology. They may affect various organs. They have at least two suckers, one oral and one ventral (Heterophyes has three). The oral sucker surrounds the mouth. The intestinal system has a blind ending. They have no blood circulation. Oxygen is absorbed by diffusion. Most trematodes are hermaphrodites and thus possess both male and female genitalia. They have a cirrus (penis). The function of the Laurer canal is unclear, but it is probably a vestigial vagina. Cross-fertilization and self-insemination are both possible. There are exceptions, e.g. schistosomes have separate sexes. After leaving the ovary, the eggs are fertilized and subsequently surrounded by yolk in the ootype (an extension of the vitelline duct). Several concentric eggshells are formed. The eggshells then undergo a chemical reaction, a kind of tanning process, which makes them tough and harder. In this way the egg acquires its typical form, and becomes more resistant to conditions in the outside world, which are often unfavorable.
Localisation
|
Intestinal lumen |
Large intestinal fluke (Fasciolopsis buski) |
|
Small intestinal flukes (Metagonimus,Heterophyes) | |
|
Lungs |
Lung fluke (Paragonimus) |
|
Bile ducts |
Large liver flukes (Fasciola hepatica and F. gigantica) |
|
Small liver flukes (Opisthorchis, Clonorchis, Dicrocoelium, Amphimerus) | |
|
Blood vessels |
Blood flukes (Schistosoma sp.) |
