CHAPTER 10 



WORMS (VERMES) 



In all these the nobler organs seem of such little use, that if 

 they be taken away the animal does not appear to feel the 

 want of them. 



Buffon's Natural History 



WORM has become a term of abuse. In the modern world it conjures 

 up a picture of a henpecked husband or the fellow who lives 

 to fight another day, or something pale and elongated, wriggling in 

 distress when a stone or a piece of decaying meat is turned upside down 

 in the sunshine. 



From the naturalist's point of view the term is applied somewhat 

 loosely to four phyla of animals : Platyhelminthes or flatworms, among 

 which are found the tapeworms and flukes ; the Nemathelminthes or 

 roundworms, which include the nematodes ; the Acanthocephala or 

 spiny-headed worms, and Annelida or segmented worms, which include 

 earthworms and leeches. 



The tapeworms, flukes and spiny-headed worms are exclusively 

 parasitic, although some of their larvae enjoy a few hours of careless 

 freedom in the water and their eggs are washed about the world in the 

 ebb and flow of urine and faeces. 



During the course of their evolution most of the parasitic worms have 

 been forced to become efficient egg machines, but this has not by itself 

 solved the problem of their survival. Despite the vast number of ova 

 they produce, both tapeworms and flukes have had to resort to other 

 methods by which their progeny can be further multiplied. Thus, by a 

 process of asexual reproduction (fragmentation of the germ cell) inside 

 the first host, one egg of a bird trematode can give rise to several 

 million free-swimming larvae, each capable of developing into a 

 complete adult. Some tapeworms bud off^ multiple individuals in the 



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