WORMS, ROTIFERS, LEECHES, POLYZOA 81 



carried on false-feet or parapodia, possess tentacles, cirri and 

 branchiae, undergo a metamorphosis, and have the sexes separate. 

 The Leeches (Hirudinea) are dwellers in fresh water, frequenting 

 ponds and streams, and also live in the sea, and in moist situa- 

 tions on land. They have oval bodies, somewhat resembling an 

 earth-worm's, and generally possess two suckers, one at each end 

 of the body. 



The Common Earth-worm (Lumbricus terrestris) belongs to the 

 Few-bristled Worms (Oligoch&ta), and is such a familiar object 

 as to call for little description here. Although the Earth-worms are 

 so common, they are not only very interesting, but they are also 

 very useful animals, for they are Nature's ploughmen, for ever 

 at work turning the soil, and are the principal agents in the forma- 

 tion of that vegetable soil which is so valuable to the agricul- 

 turist. What they are capable of accomplishing we begin to 

 realise when we come to examine the results obtained by Darwin 

 in his long and patient observations, which enabled him to demon- 

 strate that an acre of garden has, on an average, a population 

 of 53,000 worms, through whose bodies some 10 tons of soil pass 

 annually. 



Gilbert White of Selborne must also have watched and medi- 

 tated much upon the doings of the earth-worms in his garden, 

 for he has left us in his writings the following eloquent testimonial 

 to their vital importance to the land : " Earth-worms, though in 

 appearance a small and despicable link in the chain of Nature, 

 yet, if lost, would make a lamentable chasm. . . . Worms seem 

 to be the great promoters of vegetation, which would proceed but 

 lamely without them, by boring, perforating, and loosening the 

 soil, and rendering it pervious to rains and the fibres of plants, 

 by drawing straws and stalks of all kinds into it ; and, most of all, 

 by throwing up such infinite numbers of lumps of earth. . . . 

 Worms probably provide new soils for hills and slopes when the 

 rain washes the earth away. . . . The earth without worms 

 would soon become cold, hard-bound, and void of fermentation, 

 and consequently sterile." 



The body of the Earth-worm is divided up into a series of 



i rings or segments, and tapers at both ends to a blunt point. 



Slightly in front of the middle part of the body there is a thickened 



area extending over five segments and called the " saddle," or 



G 



