ANNELIDS. 



439 



Sparsely-Bristled Group, — Order OligochvETA. 



The most familiar representatives of this group are the earth-worms 

 (Liimbricida*), characterised by the numerous short segments of the body, the 

 bullet-shaped, plastic head-lobe, and the hook-like bristles which form either two 

 or four longitudinal rows, and project but slightly above the surface of the skin. 



common earth-worm, Lumhricus agricola (nat. size). 



Apart from certain thickenings of the skin, earth-worms have no special organs 

 of sense, that is to say, neither ears nor eyes, although at the same time they are 

 highly sensitive to the influence of light. Their food consists for the most part of 

 the decaying animal and vegetable matter absorbed from the soil, which they take 

 in large quantities into the alimentary canal ; but they also draw into their 

 burrows straws, feathers, leaves, bits of paper, etc., to serve for food. The muscular 

 strength required to overcome such obstacles is often very great, and no one would 

 suppose that a creature so soft, slimy, and to all appearance helpless would be 

 capable of the effort ; but the muscular system of these animals is in reality highly 

 developed, as is shown by the strenuous resistance offered to any attempt to drag 

 them from their burrows. 



In Britain there appear to be about twenty kinds belonging to three genera, of 

 which the richest in species are Alloloboj>li<>i-<i and Lumbrieus, Allurus including 

 only the square-tailed worm. Earth-worms appear to be spread over all the tropical 



Bat. size). 



and temperate pails of the world, and in some countries attain a size far surpassing 

 that of the English species; one of the largest (Microchceta r<i />/>>) being an 

 inhabitant of South Africa. The average Length of this creature is 4 or <"> feet, 



