278 DARWINISM AND THE PROBLEMS OF LIFE 



develop at once.^ This can easily happen in bed, and 

 also in other ways. One of the chief transporters of 

 them is the fly, which settles on excrements as well as 

 on food. 



But though these worms are often present in great 

 quantities, they are generally only a nuisance and very 

 rarely dangerous. The latter applies more frequently 

 to a relative of theirs, the Dochmius duodenalis. This 

 worm, somewhat larger than the oxyuris, has strong 

 jaws with which it attaches itself to the wall of the 

 intestine ; it pierces this with the stiletto it has in its 

 mouth and causes frequent hemorrhage, sometimes 

 causing death and always anaemia. The ova of the 

 parasite are ejected by the anus, and develop in mud 

 or moist earth into tiny larvae, which give fresh dochmii 

 when they re-enter the human intestines. Hence the 

 disease occurs particularly in people who are compelled 

 to drink muddy water, like the Egyptians, or any who 

 work much in moist soil, such as brick-makers. It is on 

 this account that the workmen in the St. Gothard tunnel 

 had to suffer so much from dochmii. It was through 

 the tunnel that the worm was introduced into Germany. 



In these instances we have followed a simple develop- 

 ment of parasites, but we now turn to animals with a 

 much more complicated life -story. These are the 



1 In the case of the oxyuris the eggs develop very quickly, so that 

 self-infection is always occurring, but the egg of the maw-worm needs 

 months before it will develop into a new animal if re-introduced into 

 the human body. In this case, therefore, the infection is not so direct 

 as in the oxyuris ; it usually comes about through drinking meadow- 

 water, or putting grass in the mouth, which may also bring one the 

 much more mischievous echinococcus that we will describe presently. 



